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THE
STEREOSCOPE
ITS HISTORY, THEORY, AND CONSTRUCTION
WITH ITS APPLICATION TO THE FINE AND USEFUL ARTS
AND TO EDUCATION.
SIR DAVID BREWSTER, K.H., D.C.L., F.R.S., M.R.I.A.,
VICB-PRBSIDENT OF THB ROYAL 80CIKTY OF EDINBURGH, OifB OF THE SIGHT
ASSOCIATES OF THB IMPBBIAL INSTITUTE OF FRANCE, OPFICBR OF THB
LBOION OF HONOUR, CHBYALIBB OF THB PRUSSIAN OBDBB OF MERIT,
HONORARY OB CORRESPONDING UBMBBR OF THB ACAOBHIBS
OF PBTBRSBURGH, YIBNNA, BBRLIN, COPBNHAGBN,
STOCKHOLM, BBU8SBLS, GOTTIIfOBN, MODBNA,
AND OF THB NATIONAL INSTITUTE OF
WASHINGTON, BTC.
WITH FIFTY WOOD ENGRAVINGS.
LONDON:
JOHN MURRAY, ALBEMARLE STREET.
1856.
[The Right of Translation is reserved.]
//S. /-./,
KDIHBUMH : T. COMTABLI, fEIHTI* TO BIB KAJB8TT.
CONTENTS
PA OK
Introduction, 1
Chap. I. — History op the Stereoscope, . . 5
II. — On Monocular Vision, or Vision with One
Eye, 38
III. — On Binocular Vision, or Vision with Two
Eyes, 47
IV. — Description op the Ocular, Reflecting,
and Lenticular Stereoscopes, . . 53
V.— -On the Theory op Stbbeosoopic Vision, . 76
VI. — On the Union op Similar Pictures in
Binocular Vision, .... 90
VII. — Description op different Stereoscopes, . 107
VIII. — Method op taking Pictures for the
Stereoscope, 131
IX. — On the Adaptation op the Pictures to
the Stereoscope. — Their Size, Position,
and Illumination, . . .159
X. — Application op the Stereoscope to Paint-
ing, 166
XI. — Application op the Stereoscope to Sculp-
ture, Architecture, and Engineering, . 183
XII. — Application op the Stereoscope to Na-
tural History, 189
IT CONTENTS.
PAOB
Chap. XIII.— Application op the Stereoscope to Edu-
cational Purposes, . . .193
XIV. — Application op the Stereoscope to Pub-
poses of Amusement, .... 204
XV. — On the Production op Stereoscopic
Pictures from a Single Picture, 200
XVI. — On certain Fallacies of Sight in the
Vision of Solid Bodies, .... 200
XVII. — On certain Difficulties experienced in
the Use of the Stereoscope, . 231
ON THE STEREOSCOPE.
INTRODUCTION.
The Stereoscope, a word derived from tr's^og, solid, and
axomiv, to see, is an optical instrument, of modern inven-
tion, for representing, in apparent relief and solidity, all
natural objects and all groups or combinations of objects,
by uniting into one image two plane representations of
these objects or groups as seen by each eye separately. In
its most general form the Stereoscope is a binocular instru-
ment, that is, is applied to both eyes ; but in two of its
forms it is monocular, or applied only to one eye, though
the use of the other eye, without any instrumental aid, is
necessary in the combination of the two plane pictures, or
of one plane picture and its reflected image. The Stereo-
scope, therefore, cannot, like the telescope and microscope,
be used by persons who have lost the use of one eye, and
its remarkable effects cannot be properly appreciated by
those whose eyes are not equally good.
When the artist represents living objects, or groups of
them, and delineates buildings or landscapes, or when he
2 INTRODUCTION.
copies from statues or models, lie produces apparent soli-
dity, and difference of distance from the eye, by light and
shade, by the diminished size of known objects as regulated
by the principles of geometrical perspective, and by those
variations in distinctness and colour which constitute what
has been called aerial perspective. But when all these
appliances have been used in the most skilful manner, and
art has exhausted its powers, we seldom, if ever, mistake
the plane picture for the solid which it represents. The
two eyes scan its surface, and by their distance-giving
power indicate to the observer that every point of the
picture is nearly at the same distance from his eye. But
if the observer closes one eye, and thus deprives himself
of the power of determining differences of distance by the
convergency of the optical axes, the relief of the picture
is increased. When the pictures are truthful photographs,
in which the variations of light and shade are perfectly
represented, a very considerable degree of relief and solidity
is thus obtained ; and when we have practised for a while
this species of monocular vision, the drawing, whether it
be of a statue, a living figure, or a building, will appear
to rise in its different parts from the canvas, though only
to a limited extent.
In these observations we refer chiefly to ordinary draw-
ings held in the hand, or to portraits and landscapes hung
in rooms and galleries, where the proximity of the observer,
and lights from various directions, reveal the surface of the
paper or the canvas ; for in panoramic and dioramic repre-
sentations, where the light, concealed from the observer,
is introduced in an oblique direction, and where the dis-
tance of the picture is such that the convergency of the
INTRODUCTION. 6
optic axes loses much of its distance-giving power, the
illusion is very perfect, especially when aided by correct
geometrical and aerial perspective. But when the pano-
rama is illuminated by light from various directions, and
the slightest motion imparted to the canvas, its surface
becomes distinctly visible, and the illusion instantly dis-
appears.
The effects of stereoscopic representation are of a very
different kind, and are produced by a very different cause.
The singular relief which it imparts is independent of
light and shade, and of geometrical as well as of aerial
perspective. These important accessories, so necessary in
the visual perception of the drawings in piano, avail no-
thing in the evolution of their relievo, or third dimen-
sion. They add, doubtless, to the beauty of the binocular
pictures ; but the stereoscopic creation is due solely to the
superposition of the two plane pictures by the optical appa-
ratus employed, and to the distinct and instantaneous
perception of distance by the convergency of the optic axes
upon the similar points of the two pictures which the
stereoscope has united.
If we close one eye while looking at photographic
pictures in the stereoscope, the perception of relief is still
considerable, and approximates to the binocular represen-
tation ; but when the pictures are mere diagrams consisting
of white lines upon a black ground, or black lines upon a
white ground, the relief is instantly lost by the shutting
of the eye, and it is only with such binocular pictures
that we see the true power of the stereoscope.
As an amusing and useful instrument the stereoscope
derives much of its value from photography. The most
4 INTRODUCTION.
skilful artist would have been incapable of delineating two
equal representations of a figure or a landscape as seen
by two eyes, or as viewed from two different points of
sight ; but the binocular camera, when rightly constructed,
enables us to produce and to multiply photographically the
pictures which we require, with all the perfection of that
interesting art. With this instrument, indeed, even before
the invention of the Daguerreotype and the Talbotype, we
might have exhibited temporarily upon ground glass, or
suspended in the air, the most perfect stereoscopic crea-
tions, by placing a Stereoscope behind the two dissimilar
pictures formed by the camera.
CHAPTER I.
HISTORY OP THE STEREOSCOPE.
When we look with both eyes open at a sphere, or
any other solid object, we see it by uniting into one two
pictures, one as seen by the right, and the other as seen by
the left eye. If we hold up a thin book perpendicularly,
and midway between both eyes, we see distinctly the back
of it and both sides with the eyes open. When we shut
the right eye we see with the left eye the back of the book
and the left side of it, and when we shut the left eye we
see with the right eye the back of it and the right side.
The picture of the book, therefore, which we see with both
eyes, consists of two dissimilar pictures united, namely, a
picture of the back and the left side of the book as seen
by the left eye, and a picture of the back and right side of
the book as seen by the right eye.
In this experiment with the book, and in all cases
where the object is near the eye, we not only see different
pictures of the same object, but we see different things
with each eye. Those who wear spectacles see only the
left-hand spectacle-glass with the left eye, on the left side
of the face, while with the right eye they see only the
right-hand spectacle-glass on the right side of the face,
both glasses of the spectacles being seen united midway
6 THEOREMS OF EUCLID. CHAP. I.
between the eyes, or above the nose, when both eyes are
open. It is, therefore, a fact well known to every person
of common sagacity that the pictures of bodies seen by both
eyes are formed by the union of two dissimilar pictures
formed by each.
This palpable truth was known and published by ancient
mathematicians. Euclid knew it more than two thousand
years ago, as may be seen in the 26th, 27th, and 28th
theorems of his Treatise on Optics. 1 In these theorems
he shews that the part of a sphere seen by both eyes, and
having its diameter equal to, or greater or less than the
distance between the eyes, is equal to, and greater or less
than a hemisphere ; and having previously shewn in the
23d and 24th theorems how to find the part of any sphere
that is seen by one eye at different distances, it follows,
from constructing his figure, that each eye sees different
portions of the sphere, and that it is seen by both eyes by
the union of these two dissimilar pictures.
More thm fifteen hundred years ago, the celebrated phy-
sician Galen treated the subject of binocular vision more
fully than Euclid. In the twelfth chapter of the tenth
book of his work, On the use of the different parts of the
Human Body, he has described with great minuteness the
various phenomena which are seen when we look at bodies
with both eyes, and alternately with the right and the left.
He shews, by diagrams, that dissimilar pictures of a body
are seen in each of these three modes of viewing it ;
and, after finishing his demonstration, he adds, —
" But if any person does not understand these demonstra-
1 Edit of Pena, pp. 17, 18, Paris, 1577 ; or Opera, by Gregory, pp. 619, 620.
Oxon. 1703.
CHAP. I. EXPEKTMENTS OF GALEN. 7
tions by means of lines, he will finally give his assent to
them when he has made the following experiment : —
Standing near a column, and shutting each of the eyes in
succession ; — when the right eye is shut, some of those
parts of the column which were previously seen by the right,
eye on the right side of the column, will not now be s*n
by the left eye ; and when the left eye is shut, some of
those parts which were formerly seen by the left eye on the
left side of the column, will not now be seen by the right
eye. But when we, at the same time, open both eyes,
both these will be seen, for a greater part is concealed when
we look with either of the two eyes, than when we look
with both at the same time." 1
In such distinct and unambiguous terms, intelligible to
the meanest capacity, does this illustrious writer announce
the fundamental law of binocular vision — the grand prin-
ciple of the Stereoscope, namely, that the picture of the
solid column which we see with both eyes is composed of two
dissimilar pictures, as seen by each eye separately. As the
vision of the solid column, therefore, was obtained by the
union of these dissimilar pictures, an instrument only was
wanted to take such pictures, and another to combine
them. The Binocular Photographic Camera was the one
instrument, and the Stereoscope the other.
The subject of binocular vision was studied by various
optical writers who have flourished since the time of Galen.
Baptista Porta, one of the most eminent of them, repeats,
in his work On Refraction, the propositions of Euclid on
the vision of a sphere with one and both eyes, and he
cites from Galen the very passage which we have given
1 De Usu Partium Corporis Hutnani, edit. Lugduni, 1550, p. 593.
8 EXPERIMENTS OF BAPTISTA PORTA. CHAP. I.
above on the dissimilarity of the three pictures seen by
each eye and by both. Believing that we see only with
one eye at a time, he denies the accuracy of Euclid's theo-
rems, and while he admits the correctness of the observa-
tions of Galen, he endeavours to explain them upon other
principles.
In illustrating the views of Galen on the dissimilarity of
the three pictures which are requisite in binocular vision,
he employs a much more distinct diagram than that which
is given by the Greek physician. " Let a," he says, " be the
Fig. i.
pupil of the right eye, b that of the left, and do the body
to be seen. When we look at the object with both eyes we
see dc, while with the left eye we see ef, and with the
right eye gh. But if it is seen with one eye, it will be
seen otherwise, for when the left eye b is shut, the body
cd, on the left side, will be seen in hg ; but when the right
eye is shut, the body cd will be seen in fe, whereas, when
both eyes are opened at the same time, it will be seen in cd."
These results are then explained by copying the passage
OHAP. L EXPERIMENTS OF BAPTISTA PORTA. 9
from Galen, in which he supposes the observer to repeat
these experiments when he is looking at a solid column.
In looking at this diagram, we recognise at once not
only the principle, but the construction of the stereoscope.
The double stereoscopic picture or slide is represented by
he ; the right-hand picture, or the one seen by the right ejfe,
by hp ; the left-hand picture, or the one seen by the left
eye, by ge ; and the picture of the solid column in full
relief by DC, as produced midway between the other two
dissimilar pictures, hp and ge, by their union, precisely as
in the stereoscope. 1
Galen, therefore, and the Neapolitan philosopher, who
has employed a more distinct diagram, certainly knew and
adopted the fundamental principle of the stereoscope ; and
nothing more was required, for producing pictures in full
relief than a simple instrument for uniting hp and ge, the
right and left hand dissimilar pictures of the column.
In the treatise on painting which he left behind him
in MS., 2 Leonardo da Vinci has made a distinct reference
to the dissimilarity of the pictures seen by each eye as the
reason why " a painting, though conducted with the greatest
art, and finiShed to the last perfection, both with regard
to its contours, its lights, its shadows, and its colours, can
never shew a rdievo equal to that of the natural objects,
unless these be viewed at a distance and with a single
eye," 3 which he thus demonstrates. " If an object c be
viewed by a single eye at a, all objects in the space
behind it — included, as it were, in a shadow ecp, cast by
1 Joan. Baptist® Porte Neap., Be Refraction* Optica parte, lib. v. p. 132, and
lib. vi pp. 143-5. Neap. 1593.
9 Traitata delta Pictura, Scuttura, ed Architettura. Milan, 1584.
* Dr. Smith's Compkat System qfOpticks, voL ii., Remarks, pp. 41 and 244.
10 LEONARDO DA VINCI. CHAP. L
a candle at A — are invisible to an eye at a ; but when
the other eye at b is opened, part of these objects become
visible to it ; those only being hid from both eyes that
Fig. 2.
are included, as it were, in the double shadow cd, cast by
two lights at a and B and terminated in D ; the angular
space edg, beyond d, being always visible to both eyes.
And the hidden space cd is so much the shorter as the
object c is smaller and nearer to the eyes. Thus he ob-
serves that the object c, seen with both eyes, becomes, as
it were, transparent, according to the usual definition of a
transparent thing, namely, that which hides nothing beyond
it. But this cannot happen when an object, whose breadth
is bigger than that of the pupil, is viewed by a single eye.
The truth of this observation is, therefore, evident, because
a painted figure intercepts all the space behind its apparent
place, so as to preclude the eyes from the sight of every
part of the imaginary ground behind it. Hence," continues
Dr. Smith, " we have one help to distinguish the place of
a near object more accurately with both eyes than with one,
inasmuch as we see it more detached from other objects
CHAP. I. FRANCIS AGITILONHrS. 1 1
beyond it, and more of its own surface, especially if it be
roundish."
We have quoted this passage, not from its proving that
Leonardo da Vinci was acquainted with the fact that each
eye, a, b, sees dissimilar pictures of the sphere c, but
because it has been referred to by Mr. Wheatstone as the
only remark on the subject of binocular vision which he
could find " after looking over the works of many authors
who might be expected to have made them." We think
it quite clear, however, that the Italian artist knew as
well as his commentator Dr. Smith, that each eye, a and
b, sees dissimilar parts of the sphere c. It was not his
purpose to treat of the binocular pictures of c, but his
figure proves their dissimilarity.
The subject of binocular vision was successfully studied
by Francis Aguillon or Aguilonius, 1 a learned Jesuit, who
published his Optics in 1613. In the first book of his
work, where he is treating of the vision of solids of all
forms, (de genere illorum quae rot. ffrspa (fa sterea) nuncu-
pantur,) he has some difficulty in explaining, and fails to do
it, why the two dissimilar pictures of a solid, seen by each
eye, do not, when united, give a confused and imperfect
view of it. This discussion is appended to the demon-
stration of the theorem, " that when an object is seen with
two eyes, two optical pyramids are formed whose common
base is the object itself, and whose vertices are in the
eyes," 2 and is as follows : —
" When one object is seen with two eyes, the angles at
1 OpUeorum Libri Sex Phitosophis juxta ac Mathematicu utiles. Folio. Ant-
Terpiee, 1613.
* In Fio. 1, ahf is the optical pyramid seen by the eye a, and bob the optical
pyramid seen by the eye b.
12 FRANCIS AGUILONIUS. CHAP. I.
the vertices of the optical pyramids (namely, haf, gbe, Fig.
1) are not always equal, for beside the direct view in which
the pyramids ought to be equal, into whatever direction
both eyes are turned, they receive pictures of the object
under inequal angles, the greatest of which is that which
is terminated at the nearer eye, and the lesser that which
regards the remoter eye. This, I think, is perfectly evi-
dent ; but I consider it as worthy of admiration, how it
happens that bodies seen by both eyes are not all confused
and shapeless, though we view them by the optical axes
fixed on the bodies themselves. For greater bodies, seen
under greater angles, appear lesser bodies under lesser
angles. I£ therefore, one and the same body which is in
reality greater with one eye, is seen less on account of the
inequality of the angles in which the pyramids are termi-
nated, (namely, haf, gbe, 1 ) the body itself must assuredly
be seen greater or less at the same time, and to the same
person that views it ; and, therefore, since the images in
each eye are dissimilar (minime sibi cangruunt) the repre-
sentation of the object must appear confused and disturbed
(confusa ac perturbata) to the primary sense."
" This view of the subject," he continues, " is certainly
consistent with reason, but, what is truly wonderful is,
that it is not correct, for bodies are seen clearly and dis-
tinctly with both eyes when the optic axes are converged
upon them. The reason of this, I think, is, that the bodies
do not appear to be single, because the apparent images,
which are formed from each of them in separate eyes,
exactly coalesce, (sibi miduo exacte congruurvt,) but because
i These angles are equal in this diagram and in the vision of a sphere, but they
are inequal in other bodies.
CHAP. I. FBANCIS AGUILONIUS. 13
the common sense imparts its aid equally to each eye,
exerting its own power equally in the same manner as the
eyes are converged by means of their optical axes. What-
ever body, therefore, each eye sees with the eyes conjoined,
the common sense makes a single notion, not composed of
the two which belong to each eye, but belonging and
accommodated to the imaginative faculty to which it (the
common sense) assigns it. Though, therefore, the angles of
the optical pyramids which proceed from the same object
to the two eyes, viewing it obliquely, are inequal, and
though the object appears greater to one eye and less to
the other, yet the same difference does not pass into the
primary sense if the vision is made only by the axes, as we
have said, but if the axes are converged on this side or on
the other side of the body, the image of the same body
will be seen double, as we shall shew in Book iv., on the
fallacies of vision, and the one image will appear greater
and the other less on account of the inequality of the angles
under which they are seen." 1
Such is Aguilonius's theory of binocular vision, and of
the union of the two dissimilar pictures in each eye by
which a solid body is seen. It is obviously more correct
than that of Dr. Whewell and Mr. Wheatstone. Aguilonius
affirms it to be contrary to reason that two dissimilar pictures
can be united into a clear and distinct picture, as they are
actually found to be, and he is therefore driven to call in
the aid of what does not exist, a common seme, which
rectifies the picture. Dr. Whewell and Mr. Wheatstone
have cut the Gordian knot by maintaining what is impos-
sible, that in binocular and stereoscopic vision a long line
1 Aguilonius, Opticorum, lib. ii. book xxxviii. pp. 140, 141.
14 FRANCIS AGUILONIUS. CHAP. I.
is made to coincide with a short one, and a large surface
with a small one ; and in place of conceiving this to be
done by a common sense overruling optical laws, as Agui-
lonius supposes, they give to the tender and pulpy retina,
the recipient of ocular pictures, the strange power of con-
tracting or expanding itself in order to equalize inequal
lines and inequal surfaces !
In his fourth and very interesting book, on the fallacies
of distance, magnitude, position, and figure, Aguilonius
resumes the subject of the vision of solid bodies. He
repeats the theorems of Euclid and Gassendi on the vision
of the sphere, shewing how much of it is seen by each eye,
and by both, whatever be the size of the sphere, and the
distance of the observer. At the end of the theorems, in
which he demonstrates that when the diameter of the
sphere is equal to the distance between the eyes we see
exactly a hemisphere, he gives the annexed drawing of the
mode in which the sphere is seen by each eye, and by both.
D
£
Fig. 3.
In this diagram E is the right eye and d the left, chfi the
section of that part of the sphere bc which is seen by the
right eye e, bhga the section of the part which is seen by
the left eye B, and blc the half of the great circle which is
CHAP. I. FRANCIS AGUILONIUS. 15
the section of the sphere as seen by both eyes. 1 These
three pictures of the solids are all dissimilar. The right
eye b does not see the part blcif of the sphere ; the left eye
does not see the part blcga, while the part seen with both
eyes is the hemisphere blcof, the dissimilar segments bfg,
cgf being united in its vision. 2
After demonstrating his theorems on the vision of spheres
with one and both eyes, 3 Aguilonius informs us, before he
proceeds to the vision of cylinders, that it is agreed upon
that it is not merely true with the sphere, but also with
the cylinder, the cone, and all bodies whatever, that the
part which is seen is comprehended by tangent rays, such
as bb, ec for the right eye, in Fig. 3. " For," says he,
" since these tangent lines are the outermost of all those
which can be drawn to the proposed body from the same
point, namely, that in which the eye is understood to be
placed, it clearly follows that the part of the body which is
seen must be contained by the rays touching it on all sides.
For in this part no point can be found from which a right
line cannot be drawn to the eye, by which the correct
visible form is brought out." 4
Optical writers who lived after the time of Aguilonius
seem to have considered the subject of binocular vision as
exhausted in his admirable work. Gassendi, 5 though he
treats the subject very slightly, and without any figures,
tells us that we see the left side of the nose with the left
i It is obvious that a complete hemisphere is not seen with both eyes.
2 Aguilonius, Opticarum, lib. iv. pp. 306, 307.
8 In the last of these theorems Aguilonius describes and explains, we believe for
the first time, the conversion of relief in the vision of convex and concave surfaces.
See Prop. xciv. p. 312.
* Id., Id., p. 313.
* Opera, torn. ii. p. 394. Lugduni, 1658.
16 FRANCIS AGUILONIUS. CHAP. I.
eye, and the right side of it with the right eye, — two
pictures sufficiently dissimilar. Andrew Tacquet, 1 though
he quotes Aguilonius and Gassendi on the subject of seeing
distances with both eyes, says nothing on the binocular
vision of solids ; and Smith, Harris, and Porterfield, only
touch upon the subject incidentally. In commenting on
the passage which we have already quoted from Leonardo
da Vinci, Dr. Smith says, " Hence we have one help to
distinguish the place of a near object more accurately with
both eyes than with one, inasmuch as we see it more
detached from other objects beyond it, and more of its own
surface, especially if it be roundish" 2 If any farther
evidence were required that Dr. Smith was acquainted with
the dissimilarity of the images of a solid seen by each eye,
it will be found in his experiment with a "long ruler
placed between the eyebrows, and extended directly forward
with its flat sides, respecting the right hand and the left."
" By directing the eyes to a remote object," he adds, " the
right side of the ruler seen by the right eye will appear on
the left hand, and the left side on the right hand, as repre-
sented in the figure." 3
In his Treatise on Optics, published in 1775, Mr.
Harris, when speaking of the visible or apparent figures of
objects, observes, that " we have other helps for distinguish-
ing prominences of small parts besides those by which we
distinguish distances in general, as their degrees of light
and shade, and the prospect we have round them" And by
the parallax, on account of the distance betwixt our eyes,
we can distinguish besides the front part of the two sides of
l Opera Mathmatica Optica, tribua libria exposita, p. 136.
8 Opticks, vol. ii., Remarks, pp. 41 and 245. « Id., vol. L p. 48, Fig. 196.
CHAP. I. FRANCIS AGUILONITJS. 17
a near object not thicker tJian the said distance, and this
gives a visible relievo to such objects, which helps greatly to
raise or detach them from the plane in which they lie.
Thus the nose on a face is the more remarkably raised by
our seeing both sides of it at once." l That is, the relievo
is produced by the combination of the two dissimilar pictures
given by each eye.
Without referring to a figure given by Dr. Porterfield,
in which he actually gives drawings of an object as seen
by each eye in binocular vision, 2 the one exhibiting the
object as seen endwise by the right eye, and the other the
same object as seen laterally by the left eye, we may appeal
to the experience of every optical, or even of every ordi-
nary observer, in support of the fact, that the dissimilarity
of the pictures in each eye, by which we see solid objects,
is known to those who have never read it in Galen, Porta,
or Aguilonius. "Who has not observed the fact mentioned
by Gassendi and Harris, that their left eye sees only the
left side of their nose, and their right eye the right side,
two pictures sufficiently dissimilar ? Who has not noticed,
as well as Dr. Smith, that when they look at any thin, flat
body, such as a thin book, they see both sides of it — the
left eye only the left side of it, and. the right eye only th*
right side, while the back, or the part nearest the face, is
seen by each eye, and both the sides and the back by both
the eyes ? What student of perspective is there — master
or pupil, male or female — who does not know, as certainly
as he knows his alphabet, that the picture of a chair or
table, or anything else, drawn from one point of sight, or as
i Treatise on Optics, p. 171 ; see also sect. 64. p. 113.
* Treatise on the Eye. vol i. p. 412, Plate 6, Fig. 37.
B
18 MIL ELLIOT. CHAP. I.
seen by one eye placed in that point, is necessarily dis-
similar to another drawing of the same object taken from
another point of sight, or as seen by the other eye placed
in a point 2^ inches distant from the first ? If such a
person is to be found, we might then admit that the dis-
similarity of the pictures in each eye was not known to
every student of perspective. 1
Such was the state of our knowledge of binocular vision
when two individuals, Mr. Wheatstone, and Mr. Elliot, now
Teacher of Mathematics in Edinburgh, were directing their
attention to the subject. Mr. Wheatstone communicated
an important paper on the Physiology of Vision to the
British Association at Newcastle in August 1838, and ex-
hibited an instrument called a Stereoscope, by which he
united the two dissimilar pictures of solid bodies, the
roc aregsa, (fa sterea of Aguilonius,) and thus reproduced, as
it were, the bodies themselves. Mr. Wheatstone's paper
on the subject, which had been previously read at the Royal
Society on the 21st of June, was printed in their Transac-
tions for 1838. 2
Mr. Elliot was led to the study of binocular vision in
consequence of having written an Essay, so early as 1823,
for the Class of Logic in the University of Edinburgh, " On
the means by which we obtain our knowledge of distances
by the Eye." Ever since that date he was familiar with
the idea, that the relief of solid bodies seen by the eye was
1 As Mr. Wheatstone himself describes the dissimilar pictures or drawings as
" two different projections of the same object seen from two points of sight, the
distance between which is equal to the interval between the eyes of the observer,"
it is inconceivable on what ground he could imagine himself to be the discoverer of
so palpable and notorious a fact as tbat the pictures of a body seen by two eyes —
two points of sight, must be dissimilar.
*Phil. Trans., 1838, pp. 371-394.
CHAP. I. ME. ELLIOT. 19
produced by the union of the dissimilar pictures of them in
each eye, but he never imagined that this idea was his own,
believing that it was known to every student of vision.
Previous to or during the year 1834, he had resolved to
construct an instrument for uniting two dissimilar pictures,
or of constructing a stereoscope ; but he delayed doing this
till the year 1839, when he was requested to prepare an
original communication for the Polytechnic Society, which
had been recently established in Liverpool. He was thus
induced to construct the instrument which he had projected,
and he exhibited it to his friends, Mr. Richard Adie,
optician, and Mr. George Hamilton, lecturer on chemistry
in Liverpool, who bear testimony to its existence at that
date. This simple stereoscope, without lenses or mirrors,
consisted of a wooden box 1 8 inches long, 7 broad, and 4£
deep, and at the bottom of it, or rather its farther end,
was placed a slide containing two dissimilar pictures of a
landscape as seen by each eye. Photography did not then
exist, to enable Mr. Elliot to procure two views of the
same scene, as seen by each eye, but he drew the trans-
parency of a landscape with three distances. The first and
most remote was the moon and the sky, and a stream of
water from which the moon was reflected, the two moons
being placed nearly at the distance of the two eyes, or
2£ inches, and the two reflected moons at the same dis-
tance. The second distance was marked by an old cross
about a hundred feet off ; and the third distance by the
withered branch of a tree, thirty feet from the observer. In
the right-hand picture, one arm of the cross just touched
the disc of the moon, while, in the left-hand one, it pro-
jected over one-third of the disc. The branch of the tree
20 MIL ELLIOT. CHAP. I.
touched the outline of a distant hill in the one picture, but
was " a full moon's-breadth" from it on the other. When
these dissimilar pictures were united by the eyes, a land-
scape, certainly a very imperfect one, was seen in relief,
composed of three distances.
Owing, no doubt, to the difficulty of procuring good bin-
ocular pictures, Mr. Elliot did not see that his contrivance
would be very popular, and therefore carried it no farther.
He had never heard of Mr. Wheatstone's stereoscope till he
saw his paper on Vision reprinted in the Philosophical
Magazine for March 1852, and having perused it, he was
convinced not only that Mr. Wheatstone's theory of the
instrument was incorrect, but that his claim to the disco-
very of the dissimilarity of the images in each eye had no
foundation. He was, therefore, led to communicate to the
same journal the fact of his having himself, thirteen years
before, constructed and used a stereoscope, which was still
in his possession. In making this claim, Mr. Elliot had
no intention of depriving Mr. Wheatstone of the credit
which was justly due to him ; and as the claim has been
publicly made, we have described the nature of it as a part
of scientific history.
In Mr. Wheatstone's ingenious paper of 1838, the sub-
ject of binocular vision is treated at considerable length.
He gives an account of the opinions of previous writers,
referring repeatedly to the works of Aguilonius, Gassendi,
and Baptista Porta, in the last of which the views of Galen
are given and explained. In citing the passage which
we have already quoted from Leonardo da Vinci, and
inserting the figure which illustrates it, he maintains that
Leonardo da Vinci was not aware " that the object (c in
CHAP. I. MR. WHEATSTONE. 21
Fig. 2) presented a different appearance to each eye."
" He failed" he adds, " to observe this, and no subsequent
writer, to my knowledge, has supplied the omission. The
projection of two obviously dissimilar pictures on the two
retince, when a single object is viewed, while the optic axes
converge, must therefore be regarded as a new fact in the
theory of vision" Now, although Leonardo da Vinci does
not state in so many words that he was aware of the dis-
similarity of the two pictures, the fact is obvious in his
own figure, and he was not led by his subject to state the
fact at all. But even if the fact had not stared him in
the face he must have known it from the Optics of Euclid
and the writings of Galen, with which he could not fail to
have been well acquainted. That the dissimilarity of the two
pictures is not a new fact we have already placed beyond a
doubt. The fact is expressed in words, and delineated in
drawings, by Aguilonius and Baptista Porta. It was ob-
viously known to Dr. Smith, Mr. Harris, Dr. Porterfield,
and Mr. Elliot, before it was known to Mr. Wheatstone,
and we cannot understand how he failed to observe it in
works which he has so often quoted, and in which he
professes to have searched for it.
This remarkable property of binocular vision being thus
clearly established by preceding writers, and admitted by
himself as the cause of the vision of solidity or distance,
Mr. Wheatstone, as Mr. Elliot had done before him, thought
of an instrument for uniting the two dissimilar pictures
optically, so as to produce the same result that is obtained
by the convergence of the optical axes. Mr. Elliot thought
of doing this by the eyes alone; but Mr. Wheatstone
adopted a much better method of doing it by reflexion.
22 ME. WHEATSTONE. CHAP. I.
He was thus led to construct an apparatus, to be after-
wards described, consisting of two plane mirrors, placed at
an angle of 90°, to which he gave the name of stereoscope,
anticipating Mr. Elliot both in the construction and pub-
lication of his invention, but not in the general conception
of a stereoscope.
After describing his apparatus, Mr. Wheatstone proceeds
to consider (in a section entitled, " Binocular vision of
objects of different magnitudes") " what effects will result
from presenting similar images, differing only in magnitude,
to analogous parts of the retina." " For this purpose," he
says, " two squares or circles, differing obviously but not
extravagantly in size, may be drawn on two separate pieces
of paper, and placed in the stereoscope, so that the reflected
image of each shall be equally distant from the eye by which
it is regarded. It will then be seen that notwithstanding
this difference they coalesce and occasion a single resultant
perception." The fact of coalescence being supposed to be
perfect, the author next seeks to determine the difference
between the length of two lines which the eye can force
into coalescence, or " the limits within which the single
appearance subsists." He, therefore, unites two images of
equal magnitude, by making one of them visually less from
distance, and he states that, " by this experiment, the single
appearance of two images of different size is demonstrated"
Not satisfied with these erroneous assertions, he proceeds to
give a sort of rule or law for ascertaining the relative size
of the two unequal pictures which the eyes can force into
coincidence. The inequality, he concludes, must not exceed
the difference " between the projections of the same object
when seen in the most oblique position of the eyes (t.&,
CHAP. I. MR. WHEATSTONE. 23
both turned to the extreme right or the extreme left) ordi-
narily employed." Now, this rule, taken in the sense in
which it is meant, is simply a truism. It merely states
that the difference of the pictures which the eyes can make
to coalesce is equal to the difference of the pictures which
the eyes do make to coalesce in their most oblique position ;
but though a truism it is not a truth, first, because no real
coincidence ever can take place, and, secondly, because no
apparent coincidence is effected when the difference of the
picture is greater than what is above stated.
From these principles, which will afterwards be shewn
to be erroneous, Mr. Wheatstone proceeds " to examine
why two dissimilar pictures projected on the two retina?
give rise to the perception of an object in relief." " I will
not attempt," he says, " at present to give the complete
solution of this question, which is far from being so easy
as at first glance it may appear to be, and is, indeed, one of
great complexity. I shall, in this case, merely consider the
most obvious explanations which might be offered, and shew
their insufficiency to explain the whole of the phenomena.
" It may be supposed that we see only one point of a field
of view distinctly at the same instant, the one, namely, to
which the optic axes are directed, while all other points
are seen so indistinctly that the mind does not recognise
them to be either single or double, and that the figure is
appreciated by successively directing the point of conver-
gence of the optic axes successively to a sufficient number
of its points to enable us to judge accurately of its form.
" That there is a degree of indistinctness in those parts
of the field of view to which the eyes are not immediately
directed, and which increases with the distance from that
24. . MB. WHEATSTONE. CHAP. L
point, cannot be doubted; and it is also true that the
objects there obscurely seen are frequently doubled. In
ordinary vision, it may be said, this indistinctness and
duplicity are not attended to, because the eyes shifting
continually from point to point, every part of the object is
successively rendered distinct, and the perception of the
object is not the consequence of a single glance, during
which a small part of it only is seen distinctly, but is
formed from a comparison of all the pictures successively
seen, while the eyes were changing from one point of an
object to another.
" All this is in some degree true, but were it entirely so
no appearance of relief should present itself when the eyes
remain intently fixed on one point of a binocular image in
the stereoscope. But, in performing the experiment care-
fully, it will be found, provided the picture do not extend
far beyond the centres of distinct vision, that the image is
still seen single, and in relief when in this condition." 1
In this passage the author makes a distinction between
ordinary binocular vision, and binocular vision through the
stereoscope, whereas in reality there is none. The theory
of both is exactly the same. The muscles of the two eyes
unite the two dissimilar pictures, and exhibit the solid, in
ordinary vision ; whereas in stereoscopic vision the images
are united by reflexion or refraction, the eyes in both cases
obtaining the vision of different distances by rapid and
successive convergences of the optical axes. Mr. Wheat-
stone notices the degree of indistinctness in the parts of the
picture to which the eyes are not immediately directed ; but
he does not notice the " confusion and incongruity' 1 which
1 Phil. Tram., 1838, pp. 391. 392.
CHAP. I. MR. WHEATSTONE. 25
Aguilonius says ought to exist, in consequence of some
parts of the resulting relievo being seen of one size by the
left eye alone, — other parts of a different size by the right
eye alone, and other parts by both eyes. This confusion,
however, Aguilonius, as we have seen, found not to exist,
and he ascribes it to the influence of a common sense over-
ruling the operation of physical laws. Erroneous as this
explanation is, it is still better than that of Mr. Wheatstone,
which we shall now proceed to explain.
In order to disprove the theory referred to in the pre-
ceding extract, Mr. Wheatstone describes two experiments,
which he says are equally decisive against it, the first of
them only being subject to rigorous examination. With
this view he draws " two lines about two inches long, and
inclined towards each other, on a sheet of paper, and having
caused them to coincide by converging the optic axes to a
point nearer than the paper, he looks intently on the upper
end of the resultant line without allowing the eyes to
wander from it for a moment. The entire line mil appear
single, and in its proper relief, &c .... The eyes," he
continues, " sometimes become fatigued, which causes the
line to become double at those parts to which the optic
axes are not fixed, but in such case all appearance of relief
vanishes. The same experiment may be tried with small
complex figures, but the pictures should not extend too far
beyond the centre of the retinae."
Now these experiments, if rightly made and interpreted,
are not decisive against the theory. It is not true that the
entire line appears single when the axes are converged upon
the upper end of the resultant line, and it is not true that
the disappearance of the relief when it does disappear arises
26 MB. WHEATSTONE. CHAP. I.
from the eye being fatigued. In the combination of more
complex figures, such as two similar rectilineal figures con-
tained by lines of unequal length, neither the inequalities
nor the entire figure will appear single when the axes are
converged upon any one point of it.
In the different passages which we have quoted from Mr.
Wheatstone's paper, and in the other parts of it which
relate to binocular vision, he is obviously halting between
truth and error, between theories which he partly believes,
and ill-observed facts which he cannot reconcile with them.
According to him, certain truths " may be supposed" to be
true, and other truths may be " in some degree true," but
" not entirely so ;" and thus, as he confesses, the problem
of binocular and stereoscopic vision " is indeed one of great
complexity," of which " he will not attempt at present to
give the complete solution." If he had placed a proper
reliance on the law of visible direction which he acknow-
ledges I have established, and " with which," he says, " the
laws of visible direction for binocular vision ought to con-
tain nothing inconsistent," he would have seen the impos-
sibility of the two eyes uniting two lines of inequal length ;
and had he believed in the law of distinct vision he would
have seen the impossibility of the two eyes obtaining single
vision of any more than one point of an object at a time.
These laws of vision are as rigorously true as any other
physical laws, — as completely demonstrated as the law of
gravity in Astronomy, or the law of the Sines in Optics ;
and the moment we allow them to be tampered with to
obtain an explanation of physical puzzles, we convert science
into legerdemain, and philosophers into conjurors.
Such was the state of our stereoscopic knowledge in
CHAP. I. MB. WHEATSTONE. 27
1838, after the publication of Mr. Wheatstone's interesting
and important paper. Previous to this I communicated to
the British Association at Newcastle, in August 1838, a
paper, in which I established the law of visible direction
already mentioned, which, though it had been maintained
by preceding writers, had been proved by the illustrious
D'Alembert to be incompatible with observation, and the
admitted anatomy of the human eye. At the same meet-
ing Mr. Wheatstone exhibited his stereoscopic apparatus,
which gave rise to an animated discussion on the theory of
the instrument. Dr. Whewell maintained that the retina,
in uniting, or causing to coalesce into a single resultant
impression two lines of different lengths, had the power
either of contracting the longest, or lengthening the shortest,
or what might have been suggested in order to give the
retina only half the trouble, that it contracted the long line
as much as it expanded the short one, and thus caused them
to combine with a less exertion of muscular power ! In
opposition to these views, I maintained that the retina, a
soft pulpy membrane which the smallest force tears in
pieces, had no such power, — that a hypothesis so gratuitous
was not required, and that the law of visible direction
afforded the most perfect explanation of all the stereoscopic
In consequence of this discussion, I was led to repeat
my experiments, and to inquire whether or not the eyes in
stereoscopic vision did actually unite the two lines of dif-
ferent lengths, or of different apparent magnitudes. I found
that they did not, and that no such union was required to
convert by the stereoscope two plane pictures into the appa-
rent whole from which they were taken as seen by each
28 RECENT RESEARCHES. CHAP. L
eye. These views were made public in the lectures on the
Philosophy of the Semes, which I occasionally delivered in
the College of St. Salvator and St. Leonard, St. Andrews,
and the different stereoscopes which I had invented were
also exhibited and explained.
In examining Dr. Berkeley's celebrated Theory of Vision,
I saw the vast importance of establishing the law of visible
direction, and of proving by the aid of binocular phenomena,
and in opposition to the opinion of the most distinguished
metaphysicians, that we actually see a third dimension in
space, I therefore submitted to the Royal Society of Edin-
burgh, in January 1843, a paper On the law of visible
position in single and binocular vision, and on the repre-
sentation of solid figures by the union of dissimilar plane
pictures on the retina. More than twelve years have now
elapsed since this paper was read, and neither Mr. Wheat-
stone nor Dr. Whewell have made any attempt to defend
the views which it refutes.
In continuing my researches, I communicated to the
Royal Society of Edinburgh, in April 1844, a paper On the
knowledge of distance as given by binocular vision, in which
I described several interesting phenomena produced by the
union of similar pictures, such as those which form the
patterns of carpets and paper-hangings. In carrying on
these inquiries I found the reflecting stereoscope of little
service, and ill fitted, not only for popular use, but for the
application of the instrument to various useful purposes. I
was thus led to the construction of several new stereoscopes,
but particularly to the Lenticular Stereoscope, now in uni-
versal use. They were constructed in St. Andrews and
Dundee, of various materials, such as wood, tinplate, brass,
CHAP. I. STEREOSCOPIC PORTRAITURE. 29
and of all sizes, from that now generally adopted, to a
microscopic variety which could be carried in the pocket.
New geometrical drawings were executed for them, and
binocular pictures taken by the sun were lithographed by
Mr. Schenck of Edinburgh. Stereoscopes of the lenticular
form were made by Mr. Loudon, optician, in Dundee, and
sent to several of the nobility in London, and in other
places, and an account of these stereoscopes, and of a bin-
ocular camera for taking portraits, and copying statues, was
communicated to the Royal Scottish Society of Arts, and
published in their Transactions.
It had never been proposed to apply the reflecting stereo-
scope to portraiture or sculpture, or, indeed, to any useful
purpose ; but it was very obvious, after the discovery of the
Daguerreotype and Talbotype, that binocular drawings could
be taken with such accuracy as to exhibit in the stereoscope
excellent representations in relief, both of living persons,
buildings, landscape scenery, and every variety of sculpture.
In order to shew its application to the most interesting of
these purposes, Dr. Adamson of St. Andrews, at my request,
executed two binocular portraits of himself, which were gene-
rally circulated and greatly admired. This successful appli-
cation of the principle to portraiture was communicated to the
public, and recommended as an art of great domestic interest.
After endeavouring in vain to induce opticians, both in
London and Birmingham, (where the -instrument was exhi-
bited in 1849 to the British Association,) to construct the
lenticular stereoscope, and photographers to execute binocu-
lar pictures for it, I took with me to Paris, in 1850, a very
fine instrument, made by Mr. Loudon in Dundee, with the
binocular drawings and portraits already mentioned. I shewed
30 LENTICULAR STEREOSCOPE. CHAP. L
the instrument to the Abbe Moigno, the distinguished
author of UOptique Modeiwe, to M. Soleil and his son-in-
law, M. Duboscq, the eminent Parisian opticians, and to
some members of the Institute of France. These gentlemen
saw at once the value of the instrument, not merely as one
of amusement, but as an important auxiliary in the arts of
portraiture and sculpture. M. Duboscq immediately began
to make the lenticular stereoscope for sale, and executed a
series of the most beautiful binocular Daguerreotypes of
living individuals, statues, bouquets of flowers, and objects
of natural history, which thousands of individuals flocked
to examine and admire. In an interesting article in La
Prase, 1 the Abbe Moigno gave the following account of the
introduction of the instrument into Paris : —
" In his last visit to Paris, Sir David Brewster intrusted
the models of his stereoscope to M. Jules Duboscq, son-in-
law and successor of M. Soleil, and whose intelligence, acti-
vity, and affability will extend the reputation of the
distinguished artists of the Eue de l'Odeon, 35. M. Jules
Duboscq has set himself to work with indefatigable ardour.
Without requiring to have recourse to the binocular camera,
he has, with the ordinary Daguerreotype apparatus, pro-
cured a great number of dissimilar pictures of statues, bas-
reliefs, and portraits of celebrated individuals, &c. His
stereoscopes are constructed with more elegance, and even
with more perfection, than the original English (Scotch)
instruments, and while he is shewing their wonderful effects
to natural philosophers and amateurs who have flocked to
him in crowds, there is a spontaneous and unanimous cry
of admiration."
i December 28, 1550.
CHAP. I. LENTICULAR STEREOSCOPE. 31
While the lenticular stereoscope was thus exciting much
interest in Paris, not a single instrument had been made in
London, and it was not till a year after its introduction into
France that it was exhibited in England. In the fine col-
lection of philosophical instruments which M. Duboscq con-
tributed to the Great Exhibition of 1851, and for which he
was honoured with a Council medal, he placed a lenticular
stereoscope, with a beautiful set of binocular Daguerreotypes.
This instrument attracted the particular attention of the
Queen, and before the closing of the Crystal Palace, M.
Duboscq executed a beautiful stereoscope, which I presented
to Her Majesty in his name. In consequence of this public
exhibition of the instrument, M. Duboscq received several
orders from England, and a large number of stereoscopes
were thus introduced into this country. The demand, how-
ever, became so great, that opticians of all kinds devoted
themselves to the manufacture of the instrument, and pho-
tographers, both in Daguerreotype and Talbotype, found it
a most lucrative branch of their profession, to take binocular
portraits of views to be thrown into relief by the stereo-
scope. Its application to sculpture, which I had pointed
out, was first made in France, and an artist in Paris actually
copied a statue from the relievo produced by the stereoscope.
Three years after I had published a description of the
lenticular stereoscope, and after it had been in general use
in France and England, and the reflecting stereoscope for-
gotten, 1 Mr. Wheatstone printed, in the Philosophical
Transactions for 1852, a paper on Vision, in which he says
1 " Le fait eat," says the Abbe* Moigno, " que le stereoscope par reflexion ttait
presque complement oublii, lorsque Sir David Brewster construisit son stereoscope
par refraction que nous allons dgcrire." — Cosmos, vol. i. p. 4, 1852.
32 LENTICULAR STEREOSCOPE. CHAP. I.
that he had previously used " an apparatus in which prisms
were employed to deflect the rays of light proceeding from
the pictures, so as to make them appear to occupy the same
place ;" and he adds, " I have called it the refracting
stereoscope." 1 Now, whatever Mr. Wheatstone may have
done with prisms, and at whatever time he may have done
it, I was the first person who published a description of
stereoscopes both with refracting and reflecting prisms ; and
during the three years that elapsed after he had read my
paper, he made no claim to the suggestion of prisms till
after the great success of the lenticular stereoscope. The
reason why he then made the claim, and the only reason
why we do not make him a present of the suggestion, will
appear from the following history : —
In the paper above referred to, Mr. Wheatstone says, —
" I recommend, as a convenient arrangement of the refract-
ing stereoscope for viewing Daguerreotypes of small dimen-
sions, the instrument represented, (Fig. 4,) shortened in its
length from 8 inches to 5, and lenses 5 inches focal distance,
placed before and close to the prisms." 2 Although this
refracting apparatus, which is simply a deterioration of the
lenticular stereoscope, is recommended by Mr. Wheatstone,
nobody either makes it or uses it. The semi-lenses or quarter-
lenses of the lenticular stereoscope include a virtual and ab-
solutely perfect prism, and, what is of far more consequence,
each lens is a variable lenticular prism, so that, when the
eye-tubes are placed at different distances, the lenses have
different powers of displacing the pictures. They can thus
unite pictures placed at different distances, which cannot
be done by any combination of whole lenses and prisms.
1 PhU. Trans., 1852, p. 6. * ma., pp. 9, 10.
CHAP. I. LENTICULAR STEREOSCOPE. 33
In the autumn of 1854, after all the facts about the
stereoscope were before the public, and Mr. Wheatstone in
full possession of all the merit of having anticipated Mr.
Elliot in the publication of his stereoscopic apparatus, and
of his explanation of the theory of stereoscopic relief, such
as it was, he thought it proper to revive the controversy by
transmitting to the Abbe* Moigno, for publication in Cosmos,
an extract of a letter of mine dated 27th September 1838.
This extract was published in the Cosmos of the 1 5th August
1 854, 1 with the following illogical commentary by the editor.
" Nous avons eu tort mille fois d'accorder a notre illustre
ami, Sir David Brewster, l'invention du stereoscope par refrac-
tion. M. Wheatstone, en effet, a mis entre nos mains une
lettre datee, le croirait on, du 27 Septembre 1 838, dans lequel
nous avons lu ces mots ecrits par l'illustre savant Ecossais :
* I have also stated that you promised to order for me your
stereoscope, both with reflectors and prisms. «Fai aussi dit
(a\ Lord Rosse 2 ) que vous aviez promis de commander pour
moi votre stereoscope, celui avec re'flecteurs et celui avec
prismes.' Le stereoscope par refraction est done, aussi bien
que le stereoscope par reflexion, le stereoscope de M. Wheat-
stone, qui l'avait invente* en 1838, et le faisait construire
a cette epoque pour Sir David Brewster lui-mgme. Ce que
Sir David Brewster a imaginee, et e'est une idee tres ing&
nieuse, dont M. Wheatstone ne lui disputat jamais la gloire,
e'est de former les deux prismes du stereoscope par refraction
avec les deux moiti& d'une m£me lentille."
That the reader may form a correct idea of the conduct
of Mr. Wheatstone in making this claim indirectly, and in
i Vol. v. livre viii. p. 241.
' Mr. Andrew Ross, the celebrated optician !
C
84 LENTICULAR STEREOSCOPE. CHAP. I.
a foreign journal, whose editor he has willingly misled, I
must remind him that I first saw the reflecting stereoscope
at the meeting of the British Association at Newcastle, in
the middle of August 1838. It is proved by my letter
that he and I then conversed on the subject of prisms, which
at that time he had never thought of. I suggested prisms
for displacing the pictures, and Mr. Wheatstone's natural
reply was, that they must be achromatic prisms. This fact,
if denied, may be proved by various circumstances. His
paper of 1838 contains no reference to prisms. If he had
suggested the use of prisms in August 1838, he would
have inserted his suggestion in that paper, which was then
unpublished ; and if he had only once tried a prism stereo-
scope, he never would have used another. On my return
to Scotland, I ordered from Mr. Andrew Ross one of the
reflecting stereoscopes, and one made with achromatic prisms ;
but my words do not imply that Mr. Wheatstone was the first
person who suggested prisms, and still less that he ever made
or used a stereoscope with prisms. But however this may be,
it is a most extraordinary statement, which he allows the
Abbe* Moigno to make, and which, though made a year and
a half ago, he has not enabled the Abbe* to correct, that a
stereoscope with prisms was made for me (or for any other
person) by Mr. Ross. I never saw such an instrument, or
heard of its being constructed : I supposed that after
our conversation Mr. Wheatstone might have tried achro-
matic prisms, and in 1848, when I described my single
prism stereoscope, I stated what I now find is not cor-
rect, that / believed Mr. Wheatstone had used two achro-
matic prisms. The following letter from Mr. Andrew
Boss will prove the main fact that he never constructed
CHAP. L LENTICULAR STEREOSCOPE. 35
for me, or for Mr. Wheatstone, any refracting stereo-
scope : —
44 2, Feathebstohi Buildings,
28*/* September 1854.
"Dear Sir, — In reply to yours of the 11th instant, I
beg to state that I never supplied you with a stereoscope in
which prisms were employed in place of plane mirrors. I
have a perfect recollection of being called upon either by
yourself or Professor Wheatstone, some fourteen years since,
to make achromatized prisms for the above instrument. 1
also recollect that I did not proceed to manufacture them
in consequence of the great bulk of an achromatized prism,
with reference to their power of deviating a ray of light,
and at that period glass sufficiently free from striae could
not readily be obtained, and was consequently very high-
priced. — I remain, &c. &c
" Andrew Boss.
44 To Sir David Brewster."
Upon the receipt of this letter I transmitted a copy of it
to the Abbe' Moigno, to shew him how he had been misled
into the statement, "that Mr. Wheatstone had caused a
stereoscope with prisms to be constructed for me ;" but
neither he nor Mr. Wheatstone have felt it their duty to
withdraw that erroneous statement
In reference to the comments of the Abbe Moigno, it is
necessary to state, that when he wrote them he had in his
possession my printed description of the single prism, and
other stereoscopes, 1 in which I mention my belief, now
l The Abbe" gate an abstract of this paper in the French journal La Prase,
December 28, 1850.
36 LENTICULAR STEREOSCOPE. CHAP. L
proved to be erroneous, that Mr. Wheatstone had used
achromatic prisms, so that he had, on my express authority,
the information which surprised him in my letter. The
Abbe* also must bear the responsibility of a glaring misin-
terpretation of my letter of 1838. In that letter I say
that Mr. Wheatstone promised to order certain things from
Mr. Ross, and the Abbe* declares, contrary to the express
terms of the letter, as well as to fact, that these things
were actually constructed for me. The letter, on the
contrary, does not even state that Mr. Wheatstone complied
with my request, and it does not even appear from it that
the reflecting stereoscope was made for me by Mr. Boss.
Such is a brief history of the lenticular stereoscope, of its
introduction into Paris and London, and of its application
to portraiture and sculpture. It is now in general use over
the whole world, and it has been estimated that upwards
of half a million of these instruments have been sold. A
Stereoscope Company has been established in London 2 for
the manufacture and sale of the lenticular stereoscope, and
for the production of binocular pictures for educational and
other purposes. Photographers are now employed in every
part of the globe in taking binocular pictures for the instru-
ment, — among the ruins of Pompeii and Herculaneum —
on the glaciers and in the valleys of Switzerland — among
the public monuments in the Old and the New World —
amid the shipping of our commercial harbours — in the mu-
seums of ancient and modern life — in- the sacred precincts
1 No. 54, Cheapside, and 313, Oxford Street The prize of twenty guineas which
they offered for the best short popular treatise on the Stereoscope, has been ad-
judged to Mr. Lonie, Teacher of Mathematics in the Madras Institution, St. Andrews.
The second prise was given to the Rev. R. Graham, Abernyte, Perthshire.
CHAP. L LENTICULAR STEREOSCOPE. 37
of the domestic circle — and among those scenes of the
picturesque and the sublime which are so affectionately asso-
ciated with the recollection of our early days, and amid
which, even at the close of life, we renew, with loftier sen-
timents and nobler aspirations, the youth of our being,
which, in the worlds of the future, is to be the commence-
ment of a longer and a happier existence.
38 MONOCULAR VISION. CHAP. II.
CHAPTER II.
ON MONOCULAR VISION, OR VISION WITH ONE EYE.
In order to understand the theory and construction of
the stereoscope we must be acquainted with the general
structure of the eye, with the mode in which the images
of visible objects are formed within it, and with the laws
of vision by means of which we see those objects in the
position which they occupy, that is, in the direction and
at the distance at which they exist.
Every visible object radiates, or throws out in all direc-
tions, particles or rays of light, by means of which we see
them either directly by the images formed in the eye, or
indirectly by looking at images of them formed by their
passing through a small hole, or through a lens placed in
a dark room or camera, at the end of which is a piece of
paper or ground glass to receive the image.
In order to understand this let h be a very small pin-
hole in a shutter or camera, mn, and let rtb be any
object of different colours, the upper part, r, being red, the
middle, y, yellow, and the lower part, b, blue. If a sheet
of white paper, br, is placed behind the hole H, at the
same distance as the object rb is before it, an image, br,
will be formed of the same ray and the same colours as
the object rb. As the particles or rays of light move in
CHAP. n.
MONOCULAR VISION.
39
straight lines, a red ray from the middle part of b will
pass through the hole H and illuminate the point r with
red light In like manner, rays from the middle points of
Fig. 4.
y and B will pass through h and illuminate with yellow
and blue light the points y and b. Every other point of
the coloured spaces, R, t, and b, will, in the same manner,
paint itself, as it were, on the paper, and produce a
coloured image, byr, exactly the same in form and colour
as the object bvb. If the hole h is sufficiently small no
ray from any one point of the object will interfere with or
mix with any other ray that falls upon the paper. If the
paper is held at half the distance, at by for example, a
coloured image, 6'yY, of half the size, will be formed, and
if we hold it at twice the distance, at b "r" for example, a
coloured image, b"y[ V", of twice the size, will be painted on
the paper.
As the hole h is supposed to be so small as to receive
only one ray from every point of the object, the images of the
object, viz., br> 6V, b"r", will be very faint. By widening
40 MONOCULAR VISION. CHAP. IL
the hole h, so as to admit more rays from each luminous
point of rb, the images would become brighter, but they
would become at the same time indistinct, as the rays
from one point of the object would mix with those from
adjacent points, and at the boundaries of the colours r, Y,
and b, the one colour would obliterate the other. In order,
therefore, to obtain sufficiently bright images of visible
objects we must use lenses, which have the property of
forming distinct images behind them, at a point called
their focus. If we widen the hole H, and place in it a
lens whose focus is at y, for an object at the same dis-
tance, hy, it will form a bright and distinct image, br,
of the same size as the object rb. If we remove the
lens, and place another in h, whose focus is at tf, for
a distance hy, an image, b'r 1 , half of the size of rb, will
be formed at that point ; and if we substitute for this
lens another, whose focus is at y", a distinct image, b"r ",
twice the size of the object, will be formed, the size of the
image being always to that of the object as their respective
distances from the hole or lens at h.
With the aid of these results, which any person may
confirm by making the experiments, we shall easily under-
stand how we see external objects by means of the images
formed in the eye. The human eye, a section and a front
view of which is shewn in Fig. 5, a, is almost a sphere.
Its outer membrane, abode, orMNO, Fig. 5, b, consists
of a tough substance, and is called the sclerotic coat, which
forms the white of the eye, a, seen in the front view. The
front part of the eyeball, gxt>, which resembles a small
watch-glass, is perfectly transparent, and is called the cornea.
Behind it is the iris, ca 6 e, or c in the front view, which is
chap. n.
MONOCULAR VISION.
41
a circular disc, with a hole, a 6, in its centre, called the pupil,
or black of the eye. It is, as it were, the window of the eye,
through which all the light from visible objects must pass.
Fig. 5, A.
The iris has different colours in different persons, black, bine,
ox grey; and the pupil, a 6, or h, has the power of contracting
or enlarging its size according as the light which enters it is
more or less bright. In sunlight it is very small, and in twi-
light its size is considerable. Behind the iris, and close to
it, is a doubly convex lens, df, or ll in Fig. 5, b, called
M
Fig. 5, B.
the crystalline lens. It is more convex or round on the
inner side, and it is suspended by the ciliary processes at
lc, Lcf, by which it is supposed to be moved towards and
from h, in order to accommodate the eye to different dis-
42 MONOCULAR VISION. CHAP. H.
tances, or obtain distinct vision at these distances. At the
back of the eye is a thin pulpy transparent membrane,
rr o rr, or vvv, called the retina, which, like the ground
glass of a camera obscura, receives the images of visible
objects. This membrane is an expansion of the optic nerve
o, or a in Fig.. 5 4 A, which passes to the brain, and, by a
process of whidkwe are ignorant, gives us vision of the
objects whose images are formed on its expanded surface.
The globular form of the eye is maintained by two fluids
which fill it, — the aqueous humour, which lies between the
crystalline lens and the cornea, and the vitreous humour, zz,
which fills the back of the eye.
But though we are ignorant of the manner in which the
mind takes cognizance through the brain of the images on
the retina, and may probably never know it, we can deter-
mine experimentally the laws by which we obtain, through
their images on the retina, a knowledge of the direction,
the position, and the form of external objects.
If the eye mn consisted only of a hollow ball with a
small aperture h, an inverted image, a b, of any external
object ab would be formed on the retina ror, exactly as in
Fig. 4. A ray of light from a passing through h would
strike the retina at a, and one from b would strike the
retina at b. If the hole H is very small the inverted image
ab would be very distinct, but very obscure. If the hole
were the size of the pupil the image would be sufficiently
luminous, but very indistinct. To remedy this the crystal-
line lens is placed behind the pupil, and gives distinctness
to the image ab formed in its focus. The image, however,
still remains inverted, a ray from the upper part a of the
object necessarily, falling on the lower part a of the retina,
(MAP. It MONOCULAB VISION. 43
and a ray from the lower part b of the object upon the
upper part b of the retina. Now, it has been proved by
accurate experiments that in whatever direction a ray ah a
falls upon the retina, it gives us the vision of the point a
from which it proceeds, or causes us to see that point, in a
direction perpendicular to the retina at a, the point on which
it fells. It has also been proved that the human eye is
nearly spherical, and that a line drawn perpendicular to the
retina from any point a of the image a b will very nearly
pass through the corresponding point a of the object ab, 1
so that the point A is, in virtue of this law, which is called
the Law of visible direction, seen in nearly its true direction.
When we look at any object, ab, for example, we see only
one point of it distinctly. In Fig. 5 the point d only is
seen distinctly, and every point from d to a, and from d to
B, less distinctly. The point of distinct vision on the retina
is at d, corresponding with the point d of the object which is
seen distinctly. This point d is the centre of the retina at
the extremity of the line a Ha, called the optical axis of
the eye, passing through the centre of the lens Lh, and the
centre of the pupil. The point of distinct vision d corre-
sponds with a small hole in the retina called the Foiwmen
centrale, or central hole, from its being in the centre of the
membrane. When we wish to see the points a and b, or
any othef point of the object, we turn the eye upon them,
so that their image may fall upon the central point d.
This is done so easily and quickly that every point of an
object is seen distinctly in an instant, and we obtain the
most perfect knowledge of its form, colour, and direction.
l Edinburgh Transactions, voL xv. p. 349. 1843; or Philotophical Magazine,
▼oL xxt. pp. 356, 439, May and June 1844.
44 CBTTEBIA OF DISTANCE. CHAP. XL
The law of distinct vision may be thus expressed. Vision
is most distinct when it is performed by the central point
of the retina, and the distinctness decreases with the dis-
tance from the central point. It is a carious fact, how-
ever, that the most distinct point d is the least sensitive
to light, and that the sensitiveness increases with the dis-
tance from that point. This is proved by the remarkable
fact, that when an astronomer cannot see a very minute
star by looking at it directly along the optical axis dD, he
can see it by looking away from it, and bringing its image
upon a more sensitive part of the retina.
But though we see with one eye the direction in which
any object or point of an object is situated, we do not see
its position, or the distance from the eye at which it is
placed. If a small luminous point or flame is put into a
dark room by another person, we cannot with one eye form
anything like a correct estimate of its distance. Even in
good light we cannot with one eye snuff a candle, or pour
wine into a small glass at arm's length. In monocular
vision, we learn from experience to estimate all distances,
but particularly great ones, by various means, which are
called the criteria of distance ; but it is only with both
eyes that we can estimate with anything like accuracy the
distance of objects not far from us.
The criteria of distance, by which we are enabled with
one eye to form an approximate estimate of the distance of
objects are five in number.
1. The interposition of numerous objects between the
eye and the object whose distance we are appreciating. A
distance at sea appears much shorter than the same distance
on land, marked with houses, trees, and other objects ; and
CHAP. n. CRITERIA OF -DISTANCE. 45
for the same reason, the sun and moon appear more dis-
tant when rising or setting on the horizon of a flat country,
than when in the zenith, or at great altitudes.
2. The variation in the apparent magnitude of known
objects, such as man, animals, trees, doors and windows of
houses. If one of two men, placed at different distances
from us, appears only half the size of the other, we cannot
be far wrong in believing that the smallest in appear-
ance is at twice the distance of the other. It is possible that
the one may be a dwarf, and the other of gigantic stature,
in which case our judgment would be erroneous, but even
in this case other criteria might enable us to correct it.
3. The degree of vivacity in the colours and tints of
objects.
4. The degree of distinctness in the outline and minute
parts of objects.
5. To these criteria we may add the sensation of muscular
action, or rather effort, by which we close the pupil in
accommodating the eye to near distances, and produce the
accommodation.
With all these means of estimating distances, it is only
by binocular vision, in which we converge the optical axes
upon the object, that we have the power of seeing distance
within a limited range.
But this is the only point in which Monocular is inferior
to Binocular vision. In the following respects it is superior
to it.
1. When we look at oil paintings, the varnish on their
surface reflects to each eye the light which falls upon it
from certain parts of the room. By closing one eye we
shut out the quantity of reflected light which enters it
46 CRITERIA OF DISTANCE. CHAP. II.
Pictures should always be viewed by the eye farthest from
windows or lights in the apartment, as light diminishes the
sensibility of the eye to the red rays.
2. When we view a picture with both eyes, we discover,
from the convergency of the optic axes, that the picture is
on a plane surface, every part of which is nearly equidistant
from us. But when we shut one eye, we do not make this
discovery ; and therefore the effect with which the artist
gives relief to the painting exercises its whole effect in de-
ceiving us, and hence, in monocular vision, the relievo of
the painting is much more complete.
This influence over our judgment is beautifully shewn in
viewing, with one eye, photographs either of persons, or
landscapes, or solid objects. After a little practice, the
illusion is very perfect, and is aided by the correct geome-
trical perspective and chiaroscuro of the Daguerreotype
or Talbotype. To this effect we may give the name of
Monocular Relief, which, as we shall see, is necessarily
inferior to Binocular Relief \ when produced by the stereo-
scope.
3. As it very frequently happens that one eye has not
exactly the same focal length as the other, and that, when it
has, the vision by one eye is less perfect than that by the
other, the picture formed by uniting a perfect with a less
perfect picture, or with one of a different size, must be more
imperfect than the single picture formed by one eye.
CHAP. HI. BINOCULAR VISION. 47
CHAPTER III.
ON BINOCULAR VISION, OR VISION WITH TWO EYES.
We have already seen, in the history of the stereoscope,
that in the binocular vision of objects, each eye sees a dif-
ferent picture of the same object. In order to prove this,
we require only to look attentively at our own hand held up
before us, and observe how some parts of it disappear upon
closing each eye. This experiment proves, at the same time,
in opposition to the opinion of Baptista Porta, Tacquet, and
others, that we always see two pictures of the same object
combined in one. In confirmation of this fact, we have
only to push aside one eye, and observe the image which
belongs to it separate from the other, and again unite with
it when the pressure is removed.
It might have been supposed that an object seen by both
eyes would be seen twice as brightly as with one, on the
same principle as the light of two candles combined is twice
as bright as the light of one. That this is not the case has
been long known, and Dr. Jurin has proved by experiments,
which we have carefully repeated and found correct, that the
brightness of objects seen with two eyes is only -^th part
greater than when they are seen with one eye. 1 The cause
1 Smith's Opticks, vol. ii., Bern arks, p. 107. Harris makes the difference ^th
«iSth;fl!p«ct,p. 117.
48
BINOCULAR VISION.
CHAP. m.
of this is well known. When both eyes are used, the pupils
of each contract so as to admit the proper quantity of light ;
but the moment we shut the right eye, the pupil of the left
dilates to nearly twice its size, to compensate for the loss of
light arising from the shutting of the other. 1
This beautiful provision to supply the proper quantity of
light when we can use only one eye, answers a still more
important purpose, which has escaped the notice of optical
writers. In binocular vision, as we have just seen, certain
parts of objects are seen with both eyes, and certain parts
only with one ; so that, if the parts seen with both eyes were
twice as bright, or even much brighter than the parts seen
with one, the object would appear spotted, from the different
brightness of its parts. In Fig. 6, for example, (see p. 14,)
Pig. 6.
the areas bfi and cgi, the former of which is seen only by
the left eye, d, and the latter only by the right eye, e, and
the corresponding areas on the other side of the sphere, would
be only half as bright as the portion figh, seen with
both eyes, and the sphere would have a singular appearance.
It has long been, and still is, a vexed question among
1 This variation of the pupil U mentioned by Bacon.
chap. m.
BINOCULAR VISION.
49
philosophers, how we see objects single with two eyes. Bap-
tista Porta, Tacquet, and others, got over the difficulty by
denying the fact, and maintaining that we use only one eye,
while other philosophers of distinguished eminence have
adopted explanations still more groundless. The law of
risible direction supplies us with the true explanation.
Let us first suppose that we look with both eyes, b and
l, Fig. 7, upon a luminous point, d, which we see single,
Fig. 7.
though there is a picture of it on the retina of each eye.
In looking at the point D we turn or converge the optical
axes rfHD, cWd, of each eye to the point d, an image of
which is formed at d in the right eye r, and at d! in the
left eye l. In virtue of the law of visible direction the
point d is seen in the direction dv with the eye R, and in
the direction d d with the eye l, these lines being perpen-
dicular to the retina at the points d, d'. The one image of
the point d is therefore seen lying upon the other, and con-
sequently seen single. Considering d, then, as a single
point of a visible object ab, the two eyes will see the points
a and b single by the same process of turning or converg-
D
50 BINOCULAR VISION. CHAP. HI.
ing upon them their optical axes, and so quickly does the
point of convergence pass backward and forward over the
whole object, that it appears single, though in reality only
one point of it can be seen single at the same instant.
The whole picture of the line ab, as seen with one eye,
seems to coincide with the whole picture of it as seen with
the other, and to appear single. The same is true of a
surface or area, and also of a solid body or a landscape.
Only one point of each is seen single ; but we do not
observe that other points are double or indistinct, because
the images of them are upon parts of the retina which do
not give distinct vision, owing to their distance from the
foramen or point which gives distinct vision. Hence we
see the reason why distinct vision is obtained only on one
point of the retina. Were it otherwise we should see every
other point double when we look fixedly upon one part
of an object. If in place of two eyes we had a hundred,
capable of converging their optical axes to one point, we
should, in virtue of the law of visible direction, see only
one object.
The most important advantage which we derive from
the use of two eyes is to enable us to see distance, or a
third dimension in space. That we have this power has
been denied by Dr. Berkeley, and many distinguished
philosophers, who maintain that our perception of distance
is acquired by experience, by means of the criteria already
mentioned. This is undoubtedly true for great distances,
but we shall presently see, from the effects of the stereo-
scope, that the successive convergency of the optic axes
upon two points of an object at different distances, exhibits
to us the difference of distance when we have no other
CHAP. IH. BINOCULAR VISION. 51
possible means of perceiving it. If, for example, we sup-
pose G, D, Fig. 7, to be separate points, or parts of an
object, whose distances are go, do, then if we converge
the optical axes hg, h'g upon g, and next turn them
upon d, the points will appear to be situated at g and d
at the distance gd from each other, and at the distances
og, od from the observer, although there is nothing what-
ever in the appearance of the points, or in the lights and
shades of the object, to indicate distance. That this vision
of distance is not the result of experience is obvious from
the fact that distance is seen as perfectly by children as
by adults; and it has been proved by naturalists that
animals newly born appreciate distances with the greatest
correctness. We shall afterwards see that so infallible is
our vision of near distances, that a body whose real dis-
tance we can ascertain by placing both our hands upon it,
will appear at the greater or less distance at which it is
placed by the convergency of the optical axes.
We are now prepared to understand generally, how, in
binocular vision, we see the difference between a picture
and a statue, and between a real landscape and its repre-
sentation. When we look at a picture of which every part
is nearly at the same distance from the eyes, the point of
convergence of the optical axes is nearly at the same dis-
tance from the eyes; but when we look at its original,
whether it be a living man, a statue, or a landscape, the
optical axes are converged in rapid succession upon the
nose, the eyes, and the ears, or upon objects in the fore-
ground, the middle and the remote distances in the land-
scape, and the relative distances of all these points from
the eye are instantly perceived. The binocular relkf thus
52 BINOCULAK VISION. CHAP. m.
seen is greatly superior to the monocular relief already
described.
Since objects are seen in relief by the apparent union of
two dissimilar plane pictures of them formed in each eye, it
was a supposition hardly to be overlooked, that if we could
delineate two plane pictures of a solid object, as seen
dissimilarly with each eye, and unite their images by the
convergency of the optical axes, we should see the solid of
which they were the representation. The experiment was
accordingly made by more than one person, and was found
to succeed ; but as few have the power, or rather the art,
of thus converging their optical axes, it became necessary
to contrive an instrument for doing this.
The first contrivances for this purpose were, as we have
already stated, made by Mr. Elliot and Mr. Wheatstone.
A description of these, and of others better fitted for the
purpose, will be found in the following chapter.
CHAP. IV. THE OCULAR STEREOSCOPE. 53
CHAPTER IV.
DESCRIPTION OF THE OCULAR, THE REFLECTING, AND THE
LENTICULAR STEREOSCOPES.
Although it is by the combination of two plane pic-
tures of an object, as seen by each eye, that we see the
object in relief, yet the relief is not obtained from the mere
combination or superposition of the two dissimilar pictures.
The superposition is effected by turning each eye upon the
object, but the relief is given by the play of the optic axes
in uniting, in rapid succession, similar points of the two
pictures, and placing them, for the moment, at the distance
from the observer of the point to which the axes converge.
If the eyes were to unite the two images into one, and to
retain their power of distinct vision, while they lost the
power of changing the position of their optic axes, no relief
would be produced.
This is equally true when we unite two dissimilar photo-
graphic pictures by fixing the optic axes on a point nearer
to or farther from the eye. Though the pictures apparently
coalesce, yet the relief is given by the subsequent play of
the optic axes varying their angles, and converging them-
selves successively upon, and uniting, the similar points
in each picture that correspond to different distances from
the observer.
54 THE OCULAR STEREOSCOPE. CHAP. IV.
As very few persons have the power of thus uniting, by
the eyes alone, the two dissimilar pictures of the object, the
stereoscope has been contrived to enable them to combine
the two pictures, but it is not the stereoscope, as has been
imagined, that gives the relief. The instrument is merely
a substitute for the muscular power which brings the two
pictures together. The relief is produced, as formerly, solely
by the subsequent play of the optic axes. If the relief
were the effect of the apparent union of the pictures, we
should see it by looking with one eye at the combined
binocular pictures — an experiment which could be made
by optical means; but we should look for it in vain.
The combined pictures would be as flat as the combina-
tion of two similar pictures. These experiments require to
be made with a thorough knowledge of the subject, for
when the eyes are converged on one point of the combined
picture, this point has the relief or distance from the eye,
corresponding to the angle of the optic axes, and there-
fore the adjacent points are, as it were, brought into a sort
of indistinct relief along with it ; but the optical reader will
see at once that the true binocular relief cannot be given to
any other parts of the picture, till the axes of the eyes are
converged upon them. These views will be more readily
comprehended when we have explained, in a subsequent
chapter, the theory of stereoscopic vision.
The Ocular Stereoscope.
We have already stated that objects are seen in perfect
relief when we unite two dissimilar photographic pictures of
them, either by converging the optic axes upon a point so
far in front of the pictures or so far beyond them, that two
CHAP. IV. THE OCULAR STEREOSCOPE. 55
of the four images are combined. In both these cases each
picture is seen double, and when the two innermost of the
four, thus produced, unite, the original object is seen in
relief. The simplest of these methods is to converge the
optical axes to a point nearer to us than the pictures, and
this may be best done by holding up a finger between the
eyes and the pictures, and placing it at such a distance that,
when we see it single, the two innermost of the four pic-
tures are united. If the finger is held up near the dis-
similar pictures, they will be slightly doubled, the two
images of each overlapping one other; but by bringing
the finger nearer the eye, and seeing it singly and distinctly,
the overlapping images will separate more and more till
they unite. We have, therefore, made our eyes a stereo-
scope, and we may, with great propriety, call it the Ocular
Stereoscope. If we wish to magnify the picture in relief, we
have only to use convex spectacles, which will produce the
requisite magnifying power ; or what is still better, to mag-
nify the united pictures with a powerful reading-glass. The
two single images are hid by advancing the reading-glass,
and the other two pictures are kept united with a less strain
upon the eyes.
As very few people can use their eyes in this manner,
some instrumental auxiliary became necessary, and it appears
to us strange that the simplest method of doing this did
not occur to Mr. Elliot and Mr. Wheatstone, who first
thought of giving us the help of an instrument By en-
abling the left eye to place an image of the left-hand picture
upon the right-hand picture, as seen by the naked eye, we
should have obtained a simple instrument, which might be
called the Monocular Stereoscope, and which we shall have
56
THE OCULAR STEREOSCOPE.
CHAP. IV.
occasion to describe. The same contrivance applied also
to the right eye, would make the instrument Binocular.
Another simple contrivance for assisting the eyes would have
been to furnish them with a minute opera-glass, or a small
astronomical telescope about an inch long, which, when held
in the hand or placed in a pyramidal box, would unite the
dissimilar pictures with the greatest facility and perfection.
This form of the stereoscope will be afterwards described
under the name of the Opera-Glass Stereoscope.
Description of the Ocular Stereoscope.
A stereoscope upon the principle already described, in
which the eyes alone are the agent, was contrived, in 1834,
by Mr. Elliot, as we have already had occasion to state. He
placed the binocular pictures, described in Chapter L, at
one end of a box, and without the aid either of lenses or
mirrors, he obtained a landscape in perfect relief. I have
examined this stereoscope, and have given, in Fig. 8, an
Fig. 8.
accurate though reduced drawing of the binocular pictures
executed and used by Mr. Elliot I have also united the
CHAP. IV.
THE OCULAR STEREOSCOPE.
57
two original pictures by the convergency of the optic axe*
beyond them, and have thus seen the landscape in true
relief. To delineate these binocular pictures upon stereo-
scopic principles was a bold undertaking, and establishes,
beyond all controversy, Mr. Elliot's claim to the invention
of the ocular stereoscope.
If we unite the two pictures in Fig. 8, by converging
the optio axes to a point nearer the eye than the pictures,
we shall see distinctly the stereoscopic relief, the moon
being in the remote distance, the cross in the middle dis-
tance, and the stump of a tree in the foreground.
If we place the two pictures as in Fig. 9, which is the
position they had in Mr. Elliot's box, and unite them,
Fig. 9.
by looking at a point beyond them we shall also observe
the stereoscopic relief. In this position Mr. Elliot saw the
relief without any effort, and even without being conscious
that he was not viewing the pictures under ordinary vision.
This tendency of the optic axes to a distant convergency is
so rare that I have met with it only in one person.
As the relief produced by the union of such imperfect
58 REFLECTING STEREOSCOPE. CHAP. IV.
pictures was sufficient only to shew the correctness of the
principle, the friends to whom Mr. Elliot shewed the
instrument thought it of little interest, and he therefore
neither prosecuted the subject, nor published any account
of his contrivance.
Mr. Wheatstone suggested a similar contrivance, without
either mirrors or lenses. In order to unite the pictures by
converging the optic axes to a point between them and the
eye, he proposed to place them in a box to hide the lateral
image and assist in making them unite with the naked
eyes. In order to produce the union by looking at a point
beyond the picture, he suggested the use of " a pair of
tubes capable of being inclined to each other at various
angles," the pictures being placed on a stand in front of
the tubes. These contrivances, however, though auxiliary
to the use of the naked eyes, were superseded by the
Reflecting Stereoscope, which we shall now describe.
Description of the Reflecting Stereoscope.
This form of the stereoscope, which we owe to Mr.
Wheatstone, is shewn in Fig. 10, and is described by him
in the following terms : — " a a' are two plane mirrors,
(whether of glass or metal is not stated,) about four inches
square, inserted in frames, and so adjusted that their
backs form an angle of 90° with each other ; these mirrors
are fixed by their common edge against an upright b, or,
which was less easy to represent in the drawing against
the middle of a vertical board, cut away in such a manner
as to allow the eyes to be placed before the two mirrors,
c, d are two sliding boards, to which are attached the
upright boards d, d', which may thus be removed to different
CHAP. IV.
REFLECTING STEREOSCOPE.
59
distances from the minors. In most of the experiments
hereafter to be detailed it is necessary that each upright
board shall be at the same distance from the mirror which
Fig. 10.
is opposite to it. To facilitate this double adjustment, I
employ a right and a left-handed wooden screw, r, I ; the
two ends of this compound screw pass through the nuts e, e\
which are fixed to the lower parts of the upright boards
d, d, so that by turning the screw pin p one way the two
boards will approach, and by turning them the other they
will recede from each other, one always preserving the same
distance as the other from the middle line// e, e 1 are pan-
nels to which the pictures are fixed in such manner that
their corresponding horizontal lines shall be on the same
level ; these pannels are capable of sliding backwards or
forwards in grooves on the upright boards i>, d'. The
apparatus having been described, it now remains to ex-
plain the manner of using it. The observer must place
his eyes as near as possible to the mirrors, the right eye
60 REFLECTING STEREOSCOPE. CHAP. IV.
before the right-hand mirror, and the left eye before the
left-hand mirror, and he must move the sliding pannels
e, e' to or from him till the two reflected images coincide
at the intersection of the optic axes, and form an image of
the same apparent magnitude as each of the component
pictures. The picture will, indeed, coincide when the
sliding pannels are in a variety of different positions, and,
consequently, when viewed under different inclinations of
the optic axes, but there is only one position in which
the binocular image will be immediately seen single, of its
proper magnitude, and without fatigue to the eyes, because
in this position only the ordinary relations between the
magnitude of the pictures on the retina, the inclination of
the optic axes, and the adaptation of the eye to distinct
vision at different distances, are preserved. In all the
experiments detailed in the present memoir I shall suppose
these relations to remain undisturbed, and the optic axes
to converge about six or eight inches before the eyes.
" If the pictures are all drawn to be seen with the same
inclination of the optic axes the apparatus may be simpli-
fied by omitting the screw rl, and fixing the upright boards
D, d' at the proper distance. The sliding pannels may also
be dispensed with, and the drawings themselves be made
to slide in the grooves."
The figures to which Mr. Wheatstone applied this instru-
ment were pairs of outline representations of objects of
three dimensions, such as a cube, a cone, the frustum of a
square pyramid, which is shewn on one side of e,e' in
Fig. 10, and in other figures; and he employed them, as
he observes, " for the purpose of illustration, for had either
shading or colouring been introduced it might be supposed
CHAP. IV. BEFLECTING STEREOSCOPE. 61
that the effect was wholly or in part due to these circum-
stances, whereas, by leaving them out of consideration, no
room is left to doubt that the entire effect of relief is owing
to the simultaneous perception of the two monocular pro-
jections, one on each retina."
" Careful attention," he adds, " would enable an artist
to draw and paint the two component pictures, so as
to present to the mind of the observer, in the resultant
perception, perfect identity with the object represented.
Flowers, crystals, busts, vases, instruments of various kinds,
&&, might thus be represented, so as not to be distinguished
by sight from the real objects themselves"
This expectation has never been realized, for it is obvi-
ously beyond the reach of the highest art to draw two
copies of a flower or a bust with such accuracy of outline
or colour as to produce " perfect identity," or anything
approaching to it, " with the object represented."
Photography alone can furnish us with such representa-
tions of natural and artificial objects ; and it is singular
that neither Mr. Elliot nor Mr. Wheatstone should have
availed themselves of the well-known photographic process
of Mr. Wedgewood and Sir Humphry Davy, which, as Mr.
Wedgewood remarks, wanted only " a method of preventing
the unshaded parts of the delineation from being coloured
by exposure to the day, to render the process as useful as
it is elegant." When the two dissimilar photographs were
taken they could have been used in the stereoscope in
candle-light, or in faint day-light, till they disappeared, or
permanent outlines of them might have been taken and
coloured after nature.
Mr. Fox Talbot's beautiful process of producing perma-
62 DEFECTS OF THE REFLECTING STEREOSCOPE. CHAP. IV.
nent photographs was communicated to the Royal Society
in January 1839, but no attempt was made till some
years later to make it available for the stereoscope.
In a chapter on binocular pictures, and the method of
executing them in order to reproduce, with perfect accuracy,
the objects which they represent, we shall recur to this
branch of the subject.
Upon obtaining one of these reflecting stereoscopes as
made by the celebrated optician, Mr. Andrew Ross, I
found it to be very ill adapted for the purpose of uniting
dissimilar pictures, and to be imperfect in various respects.
Its imperfections may be thus enumerated : —
1. It is a clumsy and unmanageable apparatus, rather
than an instrument for general use. The one constructed for
me was 16£ inches long, 6 inches broad, and 8£ inches
high.
2. The loss of light occasioned by reflection from the
mirrors is very great. In all optical instruments where
images are to be formed, and light is valuable, mirrors and
specula have been discontinued. Reflecting microscopes
have ceased to be used, but large telescopes, such as those
of Sir W. and Sir John Herschel, Lord Rosse, and Mr.
Lassel, were necessarily made on the reflecting principle,
from the impossibility of obtaining plates of glass of suffi-
cient size.
3. In using glass mirrors, of which the reflecting stereo-
scope is always made, we not only lose much more than
half the light by the reflections from the glass and the me-
tallic surface, and the absorbing power of the glass, but the
images produced by reflection are made indistinct by the
oblique incidence of the rays, which separates the image
CHAP. IV. DEFECTS OF THE REFLECTING STEREOSCOPE. 63
produced by the glass surface from the more brilliant image
produced by the metallic surface.
4. In all reflections, as Sir Isaac Newton states, the
errors are greater than in refraction. With glass mirrors
in the stereoscope, we have four refractions in each mirror,
and the light transmitted through twice the thickness of the
glass, which lead to two sources of error.
5. Owing to the exposure of the eye and every part of
the apparatus to light, the eye itself is unfitted for distinct
vision, and the binocular pictures become indistinct, espe-
cially if they are Daguerreotypes, 1 by reflecting the light
incident from every part of the room upon their glass or
metallic surface.
6. The reflecting stereoscope is inapplicable to the beau-
tiful binocular slides which are now being taken for the
lenticular stereoscope in every part of the world, and even
if we cut in two those on paper and silver plate, they would
give, in the reflecting instrument, converse pictures, the
right-hand part of the picture being placed on the left-hand
aide, and vice verm.
7. With transparent binocular slides cut in two, we could
obtain pictures by reflection that are not converse ; but in
using them, we would require to have two lights, one oppo-
site each of the pictures, which can seldom be obtained in
daylight, and which it is inconvenient to have at night
Owing to these and other causes, the reflecting stereo-
scope never came into use, even after photography was
capable of supplying binocular pictures.
As a set-off against these disadvantages, it has been
i Mr. Wheatstone himself says, " that it is somewhat difficult to render the two
Daguerreotypes equally risible."— PAUL Trans., 1852, p. &
64
LENTICULAR STEREOSCOPE.
CHAP. IV.
averred that in the reflecting stereoscope we can use larger
pictures, but this, as we shall shew in a future chapter, is
altogether an erroneous assertion. ,
Description of the Lenticular Stereoscope.
Having found that the reflecting stereoscope, when in-
tended to produce accurate results, possessed the defects which
I have described, and was ill fitted for general use, both
from its size and its price, it occurred to me that the union
of the dissimilar pictures could be better effected by means
of lenses, and that a considerable magnifying power would
be thus obtained, without any addition to the instrument.
If we suppose a, b, Fig. 1 1, to be two portraits, — a a por-
trait of a gentleman, as seen by the left eye of a person
Fio. n.
viewing him at the proper distance and in the best
position, and b his portrait as seen by the right eye, the
purpose of the stereoscope is to place these two pictures, or
rather their images, one above the other. The method of
CHAP. IV. LENTICULAR STEREOSCOPE. 65
doing this by lenses may be explained, to persons not ac-
quainted with optics, in the following manner : —
If we look at a with one eye through the centre of a con-
vex glass, with which we can see it distinctly at the distance
of 6 inches, which is called its focal distance, it will be seen
in its place at A. If we now move the lens from right to
left, the image of A will move towards b ; and when it is
seen through the r^rfo-hand edge of the lens, the image of
A will have reached the position c, half-way between a and
b. If we repeat this experiment with the portrait b, and
move the lens from left to right y the image of b will move
towards a ; and when it is seen through the fe/fc-hand edge of
the lens, the image of b will have reached the position c.
Now, it is obviously by the rigte-hxn& half of the lens that
we have transferred the image of a to c, and by the Z^-hand
half that we have transferred the image of b to c. If we
cut the lens in two, and place the halves — one in front
of each picture at the distance of 2 J inches — in the same
position in which they were when a was transferred to c and
b to c, they will stand as in Fig. 12, and we shall see the
Fig. 12.
portraits A and b united into one at o, and standing out in
beautiful relief, — a result which will be explained in a sub-
sequent chapter.
66 LENTICULAR STEREOSCOPE. CHAP. 17.
The same effect will be produced by quarter lenses, such
as those shewn in Fig. 13. These lenses are cut into a round
Fig. 13.
or square form, and placed in tubes, as represented at r, l
in Fig. 14, which is a drawing of the Lenticular Stereoscope.
This instrument consists of a pyramidal box, Fig. 14,
blackened inside, and having a lid, o d, for the admission of
light when required. The top of the box consists of two
parts, in one of which is the right-eye tube, R, containing
the lens o, Fig. 13, and in the other the left-eye tube, l,
containing the lens h. The two parts which hold the
lenses, and which form the top of the box, are often made
to slide in grooves, so as to suit different persons whose eyes,
placed at r, l, are more or less distant. This adjustment
may be made by various pieces of mechanism. The sim-
plest of these is a jointed parallelogram, moved by a screw
forming its longer diagonal, and working in nuts fixed on
the top of the box, so as to separate the semi-lenses, which
follow the movements of the obtuse angles of the parallelo-
gram. The tubes R, l move up and down, in order to suit
eyes of different focal lengths, but they are prevented from
turning round by a brass pin, which runs in a groove cut
through the movable tube. Immediately below the eye-
tubes r, l, there should be a groove, o, for the introduction
of convex or concave lenses, when required for very long-
CHAP. IV. LENTICULAR STEREOSCOPE. 67
sighted or short-sighted persons, or for coloured glasses and
other purposes.
If we now put the slide ab, Fig. 1 1, into the horizontal
opening at s, turning up the sneck above s to prevent it
Fig. 14.
from falling out, and place ourselves beldnd e, l, we shall
see, by looking through r with the right eye and l with
the left eye, the two images a, b united in one, and in the
same relief as the living person whom they represent. No
portrait ever painted, and no statue ever carved, approxi-
mate in the slightest degree to the living reality now before
us. If we shut the right eye R we see with the left eye
L merely the portrait a, but it has now sunk into a flat
picture, with only monocular relief. By closing the left
eye we shall see merely the portrait b, having, like the
other, only monocular relief, but a relief greater than the
best-painted pictures can possibly have, when seen even
68 LENTICULAR STEREOSCOPE. CHAP. IV.
with one eye. When we open both eyes, the two portraits
instantly start into all the roundness and solidity of life.
Many persons experience a difficulty in seeing the por-
traits single when they first look into a stereoscope, in
consequence of their eyes having less power than common
over their optic axes, or from their being more or less
distant than two and a half inches, the average distance.
The two images thus produced frequently disappear in a
few minutes, though sometimes it requires a little patience
and some practice to see the single image. We have
known persons who have lost the power of uniting the
images, in consequence of having discontinued the use of
the instrument for some months; but they have always
acquired it again after a little practice.
If the portraits or other pictures are upon opaque paper
or silver-plate, the stereoscope, which is usually held in
the left hand, must be inclined so as to allow the light of
the sky, or any other light, to illuminate every part of the
pictures. If the pictures are on transparent paper or
glass, we must shut the lid CD, and hold up the stereo-
scope against the sky or the artificial light, for which pur-
pose the bottom of the instrument is made of glass finely
ground on the outside, or has two openings, the size of each
of the binocular pictures, covered with fine paper.
In using the stereoscope the observer should always be
seated, and it is very convenient to have the instrument
mounted like a telescope, upon a stand, with a weight and
pulley for regulating the motion of the lid CD.
The lenticular stereoscope may be constructed of various
materials and in different forms. I had them made origi-
ginally of card-board, tin-plate, wood, and brass ; but wood
CHAP. IV. LENTICULAR STEREOSCOPE. <)9
is certainly the best material when cheapness is not an
object.
One of the earliest forms which I adopted was that
which is shewn in Fig. 15, as made by M. Duboscq in
Paris, and which may be called stereoscopic spectacles. The
Fig. 15.
two-eye lenses l, r are held by the handle h, so that we
can, by moving them to or from the binocular pictures,
obtain distinct vision and unite them in one. The effect,
however, is not so good as that which is produced when
the pictures are placed in a box.
The same objection applies to a form otherwise more
convenient, which consists in fixing a cylindrical or square
rod of wood or metal to c, the middle point between l and
R. The binocular slide having a hole in the middle between
the two pictures is moved along this rod to its proper dis-
tance from the lenses.
70
LENTICULAR STEREOSCOPE.
CHAP. IV.
Another form, analogous to this, but without the means
of moving the pictures, is shewn in Fig. 16, as made by
M. Duboscq. The adjustment is effected by moving the
Fig. 16.
eye-pieces in their respective tubes, and by means of a
screw-nut, shewn above the eye-pieces, they can be adapted
to eyes placed at different distances from one another.
The advantage of this form, if it is an advantage, consists
in allowing us to use larger pictures than can be admitted
into the box-stereoscope of the usual size. A box-stereo-
scope, however, of the same size, would have the same
property and other advantages not possessed by the open
instrument.
Another form of the lenticular stereoscope, under the
name of the cosmorama stereoscope, has been adopted
by Mr. Knight. The box is rectangular instead of pyra-
midal, and the adjustment to distinct vision is made by
pulling out or pushing in a part of the box, instead
of the common and better method of moving each lens
CHAP. IV. • LENTICULAR STEREOSCOPE. 71
separately. The illumination of the pictures is made in
the same manner as in the French instrument, called the
cosmorama, for exhibiting dissolving viewB. The lenses
are large in surface, which, without any reason, is supposed
to facilitate the view of the binocular pictures, and the
instrument is supported in a horizontal position upon a
stand. There is no contrivance for adjusting the distance
of the lenses to the distance between the eyes, and owing
to the quantity of light which gets into the interior of
the box, the stereoscopic picture is injured by false reflec-
tions, and the sensibility of the eyes diminished. The
exclusion of all light from the eyes, and of every other
light from the picture but that which illuminates it,
is essentially necessary to the perfection of stereoscopic
vision.
When by means of any of these instruments we have
succeeded in forming a single image of the two pictures,
we have only, as I have already explained, placed the one
picture above the other, in so far as the stereoscope is
concerned. It is by the subsequent action of the two
eyes that we obtain the desired relief. Were we to
unite the two pictures when transparent, and take a copy
of the combination by the best possible camera, the result
would be a blurred picture, in which none of the points or
lines of the one would be united with the points or lines
of the other ; but were we to look at the combination with
both eyes the blurred picture would start into relief, the
eyes uniting in succession the separate points and lines of
which it is composed.
Now, since, in the stereoscope, when looked into with
two eyes, we see the picture in relief with the same accu-
72
LENTICULAR STEREOSCOPE.
CHAP. rv.
racy as, in ordinary binocular vision, we see the same object
in relief by uniting on the retina two pictures exactly the
same as the binocular ones, the mere statement of this
fact has been regarded as the theory of the stereoscope.
We shall see, however, that it is not, and that it remains
to be explained, more minutely than we have done in
Chapter III., both how we see objects in relief in ordinary
binocular vision, and how we see them in the same relief
by uniting ocularly, or in the stereoscope, two dissimilar
images of them.
Before proceeding, however, to this subject, we must
explain the manner in which half and quarter lenses unite
the two dissimilar pictures.
In Fig. 17 is shewn a semi-lens mn, with its section
*i
a a '
Fig. 17.
m'n.' If we look at any object successively through the
portions aa'a" in the semi-lens mn, corresponding to a a' a"
in the section m'n', which is the same as in a quarter-lens,
the object will be magnified equally in all of them, but it will
be more displaced, or more refracted, towards N, by looking
through a' or a than through a or a, and most of all by
looking through a" or a", the refraction being greatest at a"
or a", less at a' or a', and still less at a or a. By means of
a semi-lens, or a quarter of a lens of the size of mn, we can,
CHAP. IV. LENTICULAR STEREOSCOPE. 73
with an aperture of the size of a, obtain three different
degrees of displacement or refraction, without any change
of the magnifying power.
If we use a thicker lens, as shewn at m'n'ww, keeping
the curvature of the surface the same, we increase the re-
fracting angle at its margin n' n, we can produce any degree
of displacement we require, either for the purposes of experi-
ment, or for the duplication of large binocular pictures.
When two half or quarter lenses are used as a stereoscope,
the displacement of the two pictures is produced in the
manner shewn in Fig. 18, where ll is the lens for the left
eye e, and l'l' that for the right eye e', placed so that the
middle points, no, n'o, of each are 2^ inches distant, like
the two eyes. The two binocular pictures which are to be
united are shewn at a b, ab, and placed at nearly the same
distance. The pictures being fixed in the focus of the lenses,
the pencils ano, A'n'o', bno, B'n'o', will be refracted at the
points n, o, n',o, and at their points of incidence on the
second surface, so as to enter the eyes, e, e / , in parallel
directions, though not shewn in the Figure. The points
a, a, of one of the pictures, will therefore be seen distinctly
in the direction of the refracted ray — that is, the pencils an,
ao, issuing from a', will be seen as if they came from a 1 ,
and the pencils bn, bo, as if they came from b', so that ab
will be transferred by refraction to a'b'. In like manner,
the picture ab will be transferred by refraction to a'b', and
thus united with a'b\
The pictures ab, ab thus united are merely circles, and
will therefore be seen as a single circle at a'b'. But if we
suppose ab to be the base of the frustum of a cone, and cd
its summit, as seen by the left eye, and the circles ab, cd
74
LENTTCTJLAB STEREOSCOPE.
CHAP. IV.
to represent the base and summit of the same solid as seen
by the right eye, then it is obvious that when the pictures of
ed and cd are similarly displaced or refracted by the lenses
ll l'l', so that cd is equal to ua! and dd' to BB*, the
circles will not be united, but will overlap one another as at
CHAP. IV. LENTICULAR STEREOSCOPE. 75
cfD', dd', in consequence of being carried beyond their
place of union. The eyes, however, will instantly unite
them into one by converging their axes to a remoter point,
and the united circles will rise from the paper, or from the
base a'b', and place the single circle at the point of con-
vergence, as the summit of the frustum of a hollow cone
whose base is a'b'. If cd, cd had been farther from one
another than ab, ab, as in Figs. 20 and 21, they would
still have overlapped though not carried up to their place
of union. The eyes, however, will instantly unite them by
converging their axes to a nearer point, and the united
circles will rise from the paper, or from the base ab, and
form the summit of the frustum of a raised cone whose
base is a'b'.
In the preceding illustration we have supposed the solid
to consist only of a base and a summit, or of parts at
two different distances from the eye ; but what is true of
two distances is true of any number, and the instant that
the two pictures are combined by the lenses they will exhibit
in relief the body which they represent. If the pictures are
refracted too little, or if they are refracted too much, so as not
to be united, their tendency to unite is so great, that they
are soon brought together by the increased or diminished
convergency of the optic axes, and the stereoscopic effect
is produced. Whenever two pictures are seen, no relief is
visible ; when only one picture is distinctly seen, the relief
must be complete.
In the preceding diagram we have not shewn the refrac-
tion at the second surface of the lenses, nor the parallelism
of the rays when they enter the eye, — facte well known
in elementary optics.
76 THEORY OF THE STEREOSCOPE. CHAP. Y.
CHAPTER V.
ON THE THEORY OF STEREOSCOPIC VISION.
Having, in the preceding chapter, described the ocular,
the reflecting, and the lenticular stereoscopes, and explained
the manner in which the two binocular pictures are com-
bined or laid upon one another in the last of these instru-
ments, we shall now proceed to consider the theory of
stereoscopic vision.
In order to understand how the two pictures, when placed
the one above the other, rise into relief we must first explain
the manner in which a solid object itself is, in ordinary vision,
seen in relief, and we shall then shew how this process takes
place in the two forms of the ocular stereoscope, and in the
lenticular stereoscope. For this purpose, let ab cd, Fig. 1 9,
be a section of the frustum of a cone, that is, a cone with its
top cut off by a plane cevg, and having aebo for its base.
In order that the figure may not be complicated, it will be
sufficient to consider how we see, with two eyes, L and r,
the cone as projected upon a plane passing through its
summit QeT>g. The points l, r being the points of sight,
draw the lines ra, rb, which will cut the plane on which
the projection is to be made in the points a, b, so that ab
will represent the line ab, and a circle, whose diameter is
a b 9 will represent the base of the cone, as seen by the right
CHAP. V.
THEORY OF THE STEREOSCOPE.
77
eye b. In like manner, by drawing la, lb, we shall find
that a' b' will represent the line ab, and a circle, whose
Fig. 19.
diameter is a'b', the base aebg, as seen by the left eye.
The summit, cevg, of the frustum being in the plane of
projection, will be represented by the circle cejyg. The
representation of the frustum a bod, therefore, upon a plane
78 THEORY OF THE STEREOSCOPE. CHAP. T.
surface, as Been by the left eye l, consists of two circles,
whose diameters are ab, cd ; and, as seen by the right eye,
of other two circles, whose diameters are aft, cd, which, in
Fig. 20, are represented by ab, od, and ab, cd. These
Fio. 20.
plane figures being also the representation of the solid on
the retina of the two eyes, how comes it that we see the
solid and not the plane pictures 1 When we look at the
point b, Fig. 19, with both eyes, we converge upon it the
optic axes lb, rb, and we therefore see the point single, and
at the distances l b, r b from each eye. When we look at the
point d, we withdraw the optic axes from B, and converge
them upon d. We therefore see the point d single, and at
the distances ld, rd from each eye ; and in like manner
the eyes run over the whole solid, seeing every point single
and distinct upon which they converge their axes, and at
the distance of the point of convergence from the observer.
During this rapid survey of the object, tbe whole of it is
seen distinctly as a solid, although every point of it is seen
double and indistinct, excepting the point upon which the
axes are for the instant converged.
From these observations it is obvious, that when we look
with both eyes at any solid or body in relief, we see more of
the right side of it by the right eye, and more of the left side
CHAP. V. THEORY OP THE STEREOSCOPE. 79
of it by the left eye. The right side of the frustum abcd,
Fig. 19, is represented by the line vb, as seen by the right
eye, and by the shorter line db', as seen by the left eye.
In like manner, the left side ac is represented by ca', as
seen by the left eye, and by the shorter line ca', as seen by
the right eye.
When the body is hollow, like a wine glass, we see more
of the right side with the left eye, and more of the left side
with the right eye.
If we now separate, as in Fig. 20, the two projections
shewn together on Fig. 19, we shall see that the two
summits, cd, cd, of the frustum are farther from one
another than the more distant bases, ab, ab, and it is true
generally that in the two pictures of any solid in relief, the
similar parts that are near the observer are more distant in
the two pictures than the remoter parts, when the plane of
perspective is beyond the object. In the binocular picture
of the human face the distance between the two noses is
greater than the distance between the two right or left
eyes, and the distance between the two right or left eyes
greater than the distance between the two remoter ears.
We are now in a condition to explain the process by
which, with the eyes alone, we can see a solid in relief by
uniting the right and left eye pictures of it,— -or the theory
ocular stereoscope. In order to obtain the proper relief
we must place the right eye picture on the left side, and
the left eye picture on the right side, as shewn in Fig. 21,
by the pictures abcd, abed, of the frustum of a cone, as
obtained from Fig. 19.
In order to unite these two dissimilar projections, we
must converge the optical axes to a point nearer the ob-
80
THEORY OF THE STEREOSCOPE.
CHAP. V.
server, or look at some point about m. Both pictures will
immediately be doubled. An image of the figure a b will
advance towards p, and an image of ab will likewise
Fio. 21.
advance towards p ; and the instant these images are united,
the frustum of a cone, which they represent, will appear in
CHAP. Y. THEORY OF THE STEREOSCOPE- 81
relief at mn, the place where the optic axes meet or cross
each other. At first the solid figure will appear in the
middle, between the two pictures from which it is formed
and of the same size, but after some practice it will appear
smaller and nearer the eye. Its smallness is an optical
illusion, as it has the same angle of apparent magnitude
as the plane figures, namely, mnh = abl ; but its position
at mn is a reality, for if we look at the point of our finger
held beyond m the solid figure will be seen nearer the eye.
The difficulty which we experience in seeing it of the size
and in the position shewn in Fig. 21, arises from its being
seen along with its two plane representations, as we shall
prove experimentally when we treat in a future chapter of
the union of similar figures by the eye.
The two images being thus superimposed, or united, we
shall now see that the combined images are seen in relief
in the very same way that in ordinary vision we saw the
real solid, abcd, Fig. 19, in relief, by the union of the
two pictures of it on the retina. From the points a,b,c,d,
a, 6, c, d, draw lines to l and b, the centres of visible direction
of each eye, and it will be seen that the circles ab, ab,
representing the base of the cone, can be united by con-
verging the optical axes to points in the line mn, and that
the circles cd, cd, which are more distant, can be united
only by converging the optic axes to points in the line op.
The points a, a, for example, united by converging the
axes to m, are seen at that point single ; the points
b, b at n single, the points c, c at o single, the points
d, d at p single, the centres s, * of the base at m single,
and the centres a',** of the summit plane at x single.
Hence the eyes l and b see the combined pictures at
F
82 THBOBY OF THE STEREOSCOPE. CHAP. V.
mn in relief, exactly in the same manner as they saw in
relief the original solid mn in Pig. 19.
In order to find the height mn of the conical frustum
thus seen, let d = distance op; d = B8, the distance of the two
points united at m ; d = a'*, the distance of the two points
united at n ; and c = lr = 2£ inches, the distance of the
eyes. Then we have —
MP =
c + d
vd>
> + d''
D d D^
np = -B* and
c + d''
If d = 9-24 inches,
c = 2-50, then
d = 2-H,
d' = 2'±2, and
mn ^ 0-283, the height of the cone.
When c = ^,mp=:^.
' 2c
As the summit plane op rises above the base mn by
the successive convergency of the optic axes to different
points in the line otfp, it may be asked how it happens
that the conical frustum still appears a solid, and the plane
op where it is, when the optic axes are converged to points
in the line mMn, so as to see the base distinctly ? The
reason of this is that the rays emanate from op exactly in
the same manner, and form exactly the same image of it,
on the two retinas as if it were the summit cd, Fig. 19,
of the real solid when seen with both eyes. The only effect
of the advance of the point of convergence from N to m is
to throw the image of n a little to the right side of the
CHAP. V. THEORY OP THE STEREOSCOPE. 83
optic axis of the left eye, and a little to the left of the
optic axis of the right eye. The summit plane op will there-
fore retain its place, and will be seen slightly doubled and
indistinct till the point of convergence again returns to it.
It has been already stated that the two dissimilar pic-
tures may be united by converging the optical axes to a
point beyond them. In order to do this, the distance
ss' of the pictures, Fig. 21, must be greatly less than the
distance of the eyes l, r, in order that the optic axes, in
passing through similar points of the two plane pictures,
may meet at a moderate distance beyond them. In order
to explain how the relief is produced in this case, let ab, cd,
a b, cd, Fig. 22, be the dissimilar pictures of the frustum
of a cone whose summit is cd, as seen by the right eye, and
cd as seen by the left eye. From l and r, as before,
draw lines through all the leading points of the pictures,
and we shall have the points a, a united at m, the points
b, b at n, the points c, c at o, and the points d, d at p,
the points s, a at m, and the points s', tf at n, forming the
cone mnop, with its base mn towards the observer, and its
summit op more remote. If the cone had been formed of
lines drawn from the outline of the summit to the outline of
the base, it would now appear hollow, the inside of it being
seen in place of the outside as before. If the pictures
ab, ab are made to change places the combined picture
would be in relief, while in the case shewn in Fig. 21
it would have been hollow. Hence the rigJti-eye view of
any solid must be placed on the left hand, and the lefLeye
view of it on the right hand, when we wish to obtain it in
relief by converging the optic axes to a point between the
pictures and the eye, and vice versa when we wish to obtain
84
THEOBY OF THE 8TBBEO8OOFE.
CHAP. V.
it in relief by converging the optic axes to a point beyond
the pictures. In every case when we wish the combined
Fig. 22.
pictures to represent a hollow, or the converse of relief,
their places must be exchanged.
CHAP. V. THEOBY OF THE STEREOSCOPE. 85
In order to find the height hn, or rather the depth of
the cone in Pig. 22, let d, d, c, c, represent the same quan-
tities as before, and we shall have
c — a
np = p ., , and
c — a '
^_ dcF nd
0P = > j
c — a c — a
When d, c, d 7 d' have the same values as before, we shall have
hn = 18-7 feet !
When c = d 9 mp will be infinite.
We have already explained how the two binocular pic-
tures are combined or laid upon one another in the lenti-
cular stereoscope. Let us now see how the relief is
obtained. The two plane pictures abc d, a b c d, in Pig. 1 8,
are, as we have already explained, combined or simply laid
upon one another by the lenses ll, l'l', and in this state
are shewn by the middle circles at a«b6, ccvd. The
images of the bases ab, ab of the cone are accurately
united in the double base ab, ab 9 but the summits of the
conical frustum remain separate, as seen at dv' 9 dd'. It is
now the business of the eyes to unite these, or rather to
make them appear as united. We have already seen how
they are brought into relief when the summits are retracted
so as to pass one another, as in Pig. 18. Let us therefore
take the case shewn in Fig. 20, where the summits cd, cd
are more distant than the bases ab, ab. The union of
these figures is instantly effected, as shewn in Fig. 23,
by converging the optic axes to points m and n succes-
sively, and thus uniting c and c and D and d, and making
these points of the summit plane appear at m and n, the
86 THEORY OP THE 8TEBEOSO0PE. CHAP. V.
points of convergence of the axes Lm, rto, and l», En.
In like manner, every pair of points in the summit
Fie. 2a
plane, and in the sides Am,B» of the frustum, are con-
verged to points corresponding to their distance from the
base a b of the original solid frustum, from which the plane
CHAP. V. THEORY OF THE STEREOSCOPE. 87
pictures abcd, abcd y were taken. We shall, therefore,
see in relief the frustum of a cone whose section is Am«B.
The theory of the stereoscope may be expressed and
illustrated in the following manner, without any reference
to binocular vision : —
1. When a drawing of any object or series of objects is
executed on a plane surface from one paint of sight, accord-
ing to the principles of geometrical perspective, every point
of its surface that is visible from the point of sight will be
represented on the plane.
2. If another drawing of the same object or series of
objects is similarly executed on the same plane from a
second point of sight, sufficiently distant from the first to
make the two drawings separate without overlapping, every
point of its surface visible from this second point of sight
will also be represented on the plane, so that we shall have
two different drawings of the object placed, at a short dis-
tance from each other, on the same plane.
M
/^ }*' f^
2
•^^...-'' / _^-^ ;: ^^-
1
p
^^^^r 2
* < ^^^^
1
o
\^ )lr' \^
Fig. 24.
3. Calling these different points of the object 1, 2, 3, 4,
&c, it will be seen from Fig. 24, in which l, e are the
88 THEORY OF THE STEREOSCOPE. CHAP. V.
two points of sight, that the distances 1, 1, on the plane
mn, of any pair of points in the two pictures representing
the point 1 of the object, will be to the distance of any
other pair 2, 2, representing the point 2, as the distances
l'p, 2'p of the points of the object from the plane mn, mul-
tiplied inversely by the distances of these points from the
points of sight l, R, or the middle point o between them.
4. If the sculptor, therefore, or the architect, or the me-
chanist, or the surveyor, possesses two such pictures, either
as drawn by a skilful artist or taken photographically, he
can, by measuring the distances of every pair of points, ob-
tain the relief or prominence of the original point, or its
distance from the plane mn or ab ; and without the use of
the stereoscope, the sculptor may model the object from
its plane picture, and the distances of every point from a
given plane. In like manner, the other artists may
determine distances in buildings, in machinery, and in the
field.
5. If the distance of the points of sight is equal to the
distance of the eyes l, r, the two plane pictures may be
united and raised into relief by the stereoscope, and thus
give the sculptor and other artists an accurate model, from
which they will derive additional aid in the execution of
their work.
6. In stereoscopic vision, therefore, when we join the
points 1, 1 by converging the optic axes to 1' in the line po,
and the points 2, 2 by converging them to 2' in the same
line, we place these points at the distances ol, o2, and
see the relief, or the various differences of distance which
the sculptor and others obtained by the method which we
have described.
CHAP. Y. THEORY OF THE STEREOSCOPE. 89
7. Hence we infer, that if the stereoscopic vision of relief
had never been thought of, the principles of the instrument
are involved in the geometrical relief which is embodied in
the two pictures of an object taken from two points of sight,
and in the prominence of every part of it obtained geome-
trically.
90 UNION OF 8IMILAB PICTURES. CHAP. VL
CHAPTER VI.
ON THE UNION OF SIMILAR PICTURES IN BINOCULAR
VISION.
In uniting by the convergency of the optic axes two
dissimilar pictures, as shewn in Fig. 18, the solid cone
mn ought to appear at mn much nearer the observer than
the pictures which compose it. I found, however, that it
never took its right position in absolute space, the base
mn of the solid seeming to rest on the same plane with
its constituent pictures ab, a b, whether it was seen by
converging the axes as in Fig. 18 or in Fig. 22. Upon
inquiring into the reason of this I found that the disturb-
ing cause was simply the simultaneous perception of other
objects in the same field of view whose distance was known
to the observer.
In order to avoid all such influences I made experiments
on large surfaces covered with similar plane figures, such as
flowers or geometrical patterns upon paper-hangings and
carpets. These figures being always at equal distances
from each other, and almost perfectly equal and similar,
the coalescence of any pair of them, effected by directing
the optic axes to a point between the paper-hanging and
the eye, is accompanied by the instantaneous coalescence of
CHAP. VI. UNION OF SIMILAE PICTUBES. 91
them all. If we, therefore, look at a papered wall without
pictures, or doors, or windows, or even at a considerable por-
tion of a wall, at the distance of three feet, and unite two of
the figures, — two flowers, for example, at the distance of
twelve inches from each other horizontally, the whole wall
or visible portion of it will appear covered with flowers as
before, but as each flower is now composed of two flowers
united at the point of convergence of the optic axes, the
whole papered wall with all its flowers will be seen sus-
pended in the air at the distance of six inches from the
observer ! At first the observer does not decide upon the
distance of the suspended wall from himself. It generally
advances slowly to its new position, and when it has taken
its place it has a very singular character. The surface of
it seems slightly curved. It has a silvery transparent
aspect. It is more beautiful than the real paper, which is
no longer seen, and it moves with the slightest motion of
the head. If the observer, who is now three feet from the
wall, retires from it, the suspended wall of flowers will fol-
low him, moving farther and farther from the real wall,
and also, but very slightly, farther and farther from the
observer. When he stands still, he may stretch out his
hand and place it on the other side of the suspended wall,
and even hold a candle on the other side of it to satisfy
himself that the ghost of the wall stands between the
candle and himself.
In looking attentively at this strange picture some of
the flowers have the aspect of real flowers. In some the
stalk retires from the plane of the picture. In others it
rises from it. One leaf will come farther out than another.
One coloured portion, red, for example, will be more pro-
92 UNION OP SIMILAR PICTURES. CHAP. VI.
minent than the blue, and the flower will thus appear
thicker and more solid, like a real flower compressed, and
deviating considerably from the plane representation of it
as seen by one eye. All this arises from slight and acci-
dental differences of distance in similar or corresponding
parts of the united figures. If the distance, for example,
between two corresponding leaves is greater than the dis-
tance between other two corresponding leaves, then the two
first when united will appear nearer the eye than the other
two, and hence the appearance of a flower in low relief, is
given to the combination.
In continuing our survey of the suspended image another
curious phenomenon often presents itself. A part of one, or
even two pieces of paper, and generally the whole length
of them from the roof to the floor, will retire behind the
general plane of the image, as if there were a recess in the
wall, or rise above it as if there were a projection, thus
displaying on a large scale the imperfection in the work-
manship which otherwise it would have been difficult to
discover. This phenomenon, or defect in the work, arises
from the paper-hanger having cut off too much of the
margin of one or more of the adjacent stripes or pieces,
or leaving too much of it, so that, in the first case, when
the two halves of a flower are joined together, part of
the middle of the flower is left out, and hence, when this
defective flower is united binocularly with the one on the
right hand of it, and the one on the left hand united with
the defective one, the united or corresponding portion being
at a less distance, will appear farther from the eye than
those parts of the suspended image which are composed of
complete flowers. The opposite effect will be produced
CHAP. VI. UNION OF SIMILAR PICTURES. 93
when the two portions of the flowers are not brought
together, but separated by a small space. All these
phenomena may be seen, though not so conveniently, with
a carpet from which the furniture has been removed. We
have, therefore, an accurate method of discovering defects
in the workmanship of paper-hangers, carpet-makers,
painters, and all artists whose profession it is to combine a
series of similar patterns or figures to form an uniformly
ornamented surface. The smallest defect in the similarity
or equality of the figures or lines which compose a pattern,
and any difference in the distance of single figures is
instantly detected, and what is very remarkable a small
inequality of distance in a line perpendicular to the axis of
vision, or in one dimension of space, is exhibited in a mag-
nified form at a distance coincident with the axis of vision,
and in an opposite dimension of space.
A little practice will enable the observer to realize and
to maintain the singular binocular vision which replaces the
real picture. 1 The occasional retention of the picture after
one eye is closed, and even after both have been closed
and quickly reopened, shews the influence of time over the
evanescence as well as over the creation of this class of
phenomena. On some occasions, a singular effect is pro-
duced. When the flowers or figures on the paper are dis-
tant six inches, we may either unite two six inches distant,
or two twelve inches distant, and so on. In the latter case,
when the eyes have been accustomed to survey the sus-
pended picture, I have found that, after shutting or open-
ing them, I neither saw the picture formed by the two
i A sheet of Queen's heads may be advantageously used to accustom the eyes to
(he union of similar figures.
94 UNION OF SIMILAR PICTURES. CHAP. VI.
flowers twelve inches distant, nor the papered wall itself,
but a picture formed by uniting all the flowers six inches
distant ! The binocular centre (the point to which the
optic axes converged, and consequently the locality of the
picture) had shifted its place, and instead of advancing to
the real wall and seeing it, it advanced exactly as much as
to unite the nearest flowers, just as in a ratchet wheel,
when the detent stops one tooth at a time ; or, to speak
more correctly, the binocular centre advanced in order to
relieve the eyes from their strain, and when the eyes were
opened, it had just reached that point which corresponded
with the union of the flowers six inches distant.
We have already seen, as shewn in Fig. 22, that when
we fix the binocular centre, that is, converge the optic axes
on a point beyond the dissimilar pictures, so as to unite
them, they rise into relief as perfectly as when the binocu-
lar centre, as shewn in Fig. 18, is fixed between the pic-
tures used and the eye. In like manner we may unite
similar pictures, but, owing to the opacity of the wall and
the floor, we cannot accomplish this with paper-hangings
and carpets. The experiment, however, may be made with
great effect by looking through transparent patterns cut out
of paper or metal, such as those in zinc which are used for
larders and other purposes. Particular kinds of trellis-work,
and windows with small squares or rhombs of glass, may
also be used, and, what is* still better, a screen might be
prepared, by cutting out the small figures from one or more
pieces of paper-hangings. The readiest means, however, of
making the experiment, is to use the cane bottom of a chair,
which often exhibits a succession of octagons with small
luminous spaces between them. To do this, place the back
CHAP. VI.
UNION OF SIMILAR PICTURES.
95
of the chair upon a table, the height of the eye either when
sitting or standing, so that the cane bottom with its lumi-
nous pattern may have a vertical position, as shewn in
Fig. 25, where mn is the real bottom of the chair with its
d i* n
■ ■■■■■
Jill
■imilMiimii M
\\
L 66 n
Fie. 25.
openings, which generally vary from half an inch to three-
fourths. Supposing the distance to be half an inch, and the
eyes, l, r, of the observer 1 2 inches distant from m n, let Lad,
hbe be lines drawn through the centres of two of the open
spaces a, b, and B.bd, rcc lines drawn through the centres of
b and c, and meeting Lad, hbe aid and e, d being the bin-
ocular centre to which the optic axes converge when we look
at it through a and b, and c the binocular centre when we
look at it through b and c. Now, the right eye, r, sees
the opening b at d, and the left eye sees the opening a at
d, so that the image at d of the opening consists of the
similar images of a and b united, and so on with all the
96 UNION OF SIMILAR PICTURES. CHAP. VI.
rest ; so that the observer at l, r no longer sees the real
pattern mn, but an image of it suspended at,mw, three
inches behind mn. If the observer now approaches mn,
the image mn will approach to him, and if he recedes,
mn will recede also, being 1£ inches behind mn when the
observer is six inches before it, and twelve inches behind
mn when the observer is forty-eight inches before it, the
image mn moving from mn with a velocity one-fourth of
that with which the observer recedes.
The observer resuming the position in the figure where
his eyes, l,r, are twelve inches distant from mn, let us
consider the important results of this experiment. If he
now grasps the cane bottom at mn, his thumbs pressing
upon mn, and his fingers trying to grasp mn, he will then
feel what he does not see, and see what he does not feel 1
The real pattern is absolutely invisible at mn, where he
feels it, and it stands fixed at mn. The fingers may be passed
through and through between the real and the false image,
and beyond it, — now seen on this side of it, now in the
middle of it, and now on the other side of it. If we next
place the palms of each hand upon mn, the real bottom of
the chair, feeling it all over, the result will be the same.
No knowledge derived from touch — no measurement of real
distance — no actual demonstration from previous or subse-
quent vision, that there is a real solid body at mn, and
nothing at all at mn, will remove or shake the infallible
conviction of the sense of sight that the cane bottom is at
mn, and that dL or d& is its real distance from the ob-
server. If the binocular centre be now drawn back to m n,
the image seen at mn will disappear, and the real object be
seen and felt at mn. If the binocular centre be brought
CHAP. VI. TOION OF SIMILAE PICTUEES. 97
further back to /, that is, if the optic axes are converged
to a point nearer the observer than the object, as illustrated
by Fig. 18, the cane bottom mn will again disappear, and
will be seen at uv, as previously explained.
This method of uniting small similar figures is more
easily attained than that of doing it by converging the
axes to a point between the eye and the object. It puts a
very little strain upon the eyes, as we cannot thus unite
figures the distance of whose centre is equal to or exceeds
2£ inches, as appears from Fig. 22.
In making these experiments, the observer cannot fail to
be struck with the remarkable fact, that though the open-
ings mn, mn, uv, have all the same apparent or angular
magnitude, that is, subtend the same angle at the eye,
viz., djjCy dne, yet those at mn appear larger, and those
at uv smaller, than those at mn. If we cause the image
mn to recede and approach to us, the figures in mn will
invariably increase at they recede, and those in uv diminish
as they approach the eye, and their visual magnitudes, as
we may call them, will depend on the respective distances
at which the observer, whether right or wrong in his esti-
mate, conceives them to be placed, — a result which is finely
illustrated by the different size of the moon when seen in
the horizon and in the meridian. The fact now stated is
a general one, which the preceding experiments demonstrate ;
and though our estimate of magnitude thus formed is erro-
neous, yet it is one which neither reason nor experience is
able to correct.
It is a curious circumstance, that, previous to the publi-
cation of these experiments, no examples have been recorded
of false estimates of the distance of near objects in conse-
G
98 UNION OF SIMILAB PICTUBES. CHAP. VX
quence of the accidental binocular union of similar images.
In a room where the paper-hangings have a small pattern,
a short-sighted person might very readily turn his eyes on
the wall when their axes converged to some point between
him and the wall, which would unite one pair of the similar
images, and in this case he would see the wall nearer him
than the real wall, and moving with the motion of his
head. In like manner a long-sighted person, with his opti-
cal axes converged to a point beyond the wall, might see
an image of the wall more distant, and moving with the
motion of his head ; or a person who has taken too much
wine, which often fixes the optical axes in opposition to the
will, might, according to the nature of his sight, witness
either of the illusions above mentioned.
Illusions of both these kinds, however, have recently
occurred. A friend to whom I had occasion to shew the
experiments, and who is short-sighted, mentioned to me
that he had on two occasions been greatly perplexed by the
vision of these suspended images. Having taken too much
wine, he saw the wall of a papered room suspended near
him in the air ; and on another occasion, when kneeling,
and resting his arms on a cane-bottomed chair, he had fixed
his eyes on the carpet, which had accidentally united the
two images of the open octagons, and thrown the image of
the chair bottom beyond the plane on which he rested his
arms.
After hearing my paper on this subject read at the Royal
Society of Edinburgh, Professor Christison communicated
to me the following interesting case, in which one of the phe-
nomena above described was seen by himself : — " Some years
ago," he observes, " when I resided in a house where several
CHAP. VI. UNION OP SIMILAR PICTURES. 99
rooms are papered with rather formally recurring patterns,
and one in particular with stars only, I used occasionally to
be much plagued with the wall suddenly standing out upon
me, and waving, as you describe, with the movements of the
head. I was sensible that the cause was an error as to the
point of union of the visual axes of the two eyes ; but I
remember it sometimes cost me a considerable effort to
rectify the error ; and I found that the best way was to
increase still more the deviation in the first instance. As
this accident occurred most frequently while I was recover-
ing from a severe attack of fever, I thought my near-sighted
eyes were threatened with some new mischief; and this
opinion was justified in finding that, after removal to my
present house, where, however, the papers have no very
formal pattern, no such occurrence has ever taken place.
The reason is now easily understood from your researches." 1
Other cases of an analogous kind have been communi-
cated to me ; and very recently M. Soret of Geneva, in
looking through a trellis-work in metal stretched upon a
frame, saw the phenomenon represented in Fig. 25, and
has given the same explanation of it which I had published
long before. 2
Before quitting the subject of the binocular union of
similar pictures, I must give some account of a series of
curious phenomena which I observed by uniting the images
of lines meeting at an angular point when the eye is placed
at different heights above the plane of the paper, and at
different distances from the angular point.
i See Edin. Transactions, 1846, vol. xv. p 663, and Phil Mag., May 1847, vol
zxx. p. 305.
2 BibL Universale, October 1855, p. 136.
100
BINOCULAK UNION OF LINES.
CHAP. VI.
Let ac, bc, Fig. 26, be two lines meeting at c, the
plane passing through them being the plane of the paper,
and let them be viewed by the eyes successively placed at
Fio. 26.
e"', e", £*, and e, at different heights in a plane, gmn, per-
pendicular to the plane of the paper. Let R be the right
eye, and l the left eye, and when at e"', let them be strained
so as to unite the points a, b. The united image of these
points will be seen at the binocular centre d'", and the
united lines ac, bc, will have the position d'"c. In like
manner, when the eye descends to e", e 7 , e, the united
image d'"c will rise and diminish, taking the positions d"c,
d'c, dc, till it disappears on the line cm, when the eyes
reach m. If the eye deviates from the vertical plane gmn,
the united image will also deviate from it, and is always in
a plane passing through the common axis of the two eyes
and the line g m.
CHAP. VI.
BINOCULAR UNION OF LINES.
101
If at any altitude em, the eye advances towards acb in
the line eg, the binocular centre d will also advance towards
acb in the line eg, and the image dc will rise, and become
shorter as its extremity r> moves along dg, and, after pass-
ing the perpendicular to ge, it will increase in length. If
the eye, on the other hand, recedes from acb in the line
ge, the binocular centre d will also recede, and the image
dc will descend to the plane cm, and increase in length.
The preceding diagram is, for the purpose of illustration,
drawn in a sort of perspective, and therefore does not give
the true positions and lengths of the united images. This
defect, however, is remedied in Fig. 27, where e, e', e", e"'
IT
is the middle point between the two eyes, the plane gmn
being, as before, perpendicular to the plane passing through
acb. Now, as the distance of the eye from g is supposed
to be the same, and as ab is invariable as well as the
distance between the eyes, the distance of the binocular
102 BINOCULAE UNION OP UNE8. CHAP. VI.
centres o, d, d', d", d'", p from o, will also be invariable,
and lie in a circle odp, whose centre is G, and whose
radius is oo, the point o being determined by the for-
mula oo = QD = ^ff * j -fjj Hence, in order to find the
binocular centres d, rV, d", d'", &c, at any altitude, e, tf, &c,
we have only to join eg, tf g, &c, and the points of inter-
section d, d', &c, will be the binocular centres, and the
lines dc, d'c, &c, drawn to c, will be the real lengths and
inclinations of the united images of the lines ac, bc.
When go is greater than gc there is obviously some
angle a, or e" g m, at which d"c is perpendicular to gc.
This takes place when Cos. a = j!^. When o coincides
with c, the images cd, cd', &c, will have the same posi-
tions and magnitudes as the chords of the altitudes a of
the eyes above the plane gc. In this case the raised or
united images will just reach the perpendicular when the
eye is in the plane gcm, for since gc = go, Cos. a=1
and a = 0.
When the eye at any position, e" for example, sees the
points a and b united at d", it sees also the whole lines
ac, bc forming the image r>"c. The binocular centre
must, therefore, run rapidly along the line d"c ; that is,
the inclination of the optic axes must gradually diminish
till the binocular centre reaches c, when all strain is re-
moved. The vision of the image d"c, however, is carried
on so rapidly that the binocular centre returns to D" with-
out the eye being sensible of the removal and resumption
of the strain which is required in maintaining a view of
the united image d" c. If we now suppose a b to diminish,
the binocular centre will advance towards G, and the length
CHAP. VI. BINOCULAR UNION OP LINES. 103
and inclination of the united images DC, D'c, &c, will
diminish also, and vice versd. If the distance rl (Fig. 26)
between the eyes diminishes, the binocular centre will
retire towards e, and the length and inclination of the
images will increase. Hence persons with eyes more or
less distant will see the united images in different places
and of different sizes, though the quantities a and ab be
invariable.
While the eyes at e" are running along the lines ac,
bc, let us suppose them to rest upon the points ab equi-
distant from c. Join a b y and from the point g, where ab
intersects oc, draw the line #e", and find the point d'
from the formula gd' = j ^V < R g ^ - Hence the two points a, b
will be united at d\ and when the angle e"gc is such that
the line joining d and c is perpendicular to gc, the line
joining d"c will also be perpendicular to gc, the loci of the
points D"cf , &c, will be in that perpendicular, and the image
dc, seen by successive movements of the binocular centre
from d" to c, will be a straight line.
In the preceding observations we have supposed that
the binocular centre d", &c, is between the eye and the
lines ac, bc ; but the points a, c, and all the other points
of these lines, may be united by fixing the binocular centre
beyond ab. Let the eyes, for example, be at e" ; then if
we unite a. b when the eyes converge to a point, A", (not
seen in the Figure) beyond g, we shall have GA" = J j^zHf jj ;
and if we join the point A" thus found and c, the line A'c
will be the united image of ac and bc, the binocular centre
ranging from a" to c, in order to see it as one line. In
like manner, we may find the position and length of the
104 BINOCULAB UNION OF UNES. CHAP. VL
image A'"c, A'c, and Ac, corresponding to the position of
the eyes at e'"e and e. Hence all the united images of ac,
bc, viz., ca'", ca", &c, will lie below the plane of abc,
and extend beyond a vertical line no continued ; and they
will grow larger and larger, and approximate in direction
to cg as the eyes descend from e"' to m. When the eyes
are near to M, and a little above the plane of abc, the line,
when not carefully observed, will have the appearance of
coinciding with cg, but stretching a great way beyond g.
This extreme case represents the celebrated experiment
with the compasses, described by Dr. Smith, and referred
to by Professor Wheatstone. He took a pair of compasses,
which may be represented by acb, ab being their points,
ac, bc their legs, and c their joint ; and having placed his
eyes about e, above their plane, he made the following
experiment : — " Having opened the points of a pair of
compasses somewhat wider than the interval of your eyes,
with your arm extended, hold the head or joint in the ball
of your hand, with the points outwards, and equidistant
from your eyes, and somewhat higher than the joint. Then
fixing your eyes upon any remote object lying in the plane
that bisects the interval of the points, you will first per-
ceive two pair of compasses, (each by being doubled with
their inner legs crossing each other, not unlike the old
shape of the letter W.) But by compressing the legs with
your hand the two inner points will come nearer to each
other ; and when they unite (having stopped the compres-
sion) the two inner legs will also entirely coincide and
bisect the angle under the outward ones, and will appear
more vivid, thicker, and larger, than they do, so as to
reach from your hand to the remotest object in view even
CHAP. VI. BINOCULAR UNION OF LINES. 105
in the horizon itself, if the points be exactly coincident." 1
Owing to his imperfect apprehension of the nature of this
phenomenon, Dr. Smith has omitted to notice that the
united legs of the compasses lie below the plane of abc,
and that they never can extend further than the binocular
centre at which their points a and b are united.
There is another variation of these experiments which
possesses some interest, in consequence of its extreme case
having been made the basis of a new theory of visible
direction, by the late Dr. Wells. 2 Let us suppose the eyes
of the observer to advance from e to n, and to descend
along the opposite quadrant on the left hand of no, but
not drawn in Fig. 27, then the united image of ac, bc will
gradually descend towards cg, and become larger and
larger. When the eyes are a very little above the plane of
abc, and so far to the left hand of ab that ca points
nearly to the left eye and cb to the right eye, then we
have the circumstances under which Dr. Wells made the
following experiment : — " If we hold two thin rules in
such a manner that their sharp edges (ac, bc in Fig. 27)
shall be in the optic axes, one in each, or rather a little
below them, the two edges will be seen united in the common
axis, (gc in Fig. 27 ;) and this apparent edge will seem of
the same length with that of either of the real edges, when
seen alone by the eye in the axis of which it is placed."
This experiment, it will be seen, is the same with that of
Dr. Smith, with this difference only, that the points of the
compasses are directed towards the eyes. like Dr. Smith
Dr. Wells has omitted to notice that the united image
i Smith's Opticks, vol. ii. p. 388, § 977.
9 Essay on Single Vision, £&, p. 44.
106 BINOCULAR UNION OF UNB8. CHAP. VL
rises above gh, and he commits the opposite error of Dr.
Smith, in making the length of the united image too short
If in this form of the experiment we fix the binocular
centre beyond c, then the united images of ac, and bc
descend below go, and vary in their length, and in their
inclination to gc, according to the height of the eye above
the plane of abc, and its distance from ab.
CHAP. VH. TUBULAR REFLECTING STEREOSCOPE. 107
CHAPTEE VII.
DESCRIPTION OF DIFFERENT STEREOSCOPES.
Although the lenticular stereoscope has every advantage
that such an instrument can possess, whether it is wanted
for experiments on binocular vision — for assisting the artist
by the reproduction of objects in relief or for the purposes
of amusement and instruction, yet there are other forms of
it which have particular properties, and which may be con-
structed without the aid of the optician, and of materials
within the reach of the humblest inquirers. The first of
these j
1. The Tubular Reflecting Stereoscope.
In this form of the instrument, shewn in Fig. 28, the
pictures are seen by reflexion from two specula or prisms
placed at an angle of 90°, as in Mr. Wheatstone's instrument.
In other respects the two instruments are essentially different.
In Mr. Wheatstone's stereoscope he employs two mirrors,
each four inches square — that is, he employs thirty-two
square inches of reflecting surface, and is therefore under
the necessity of employing glass mirrors, and making a
clumsy, unmanageable, and unscientific instrument, with all
the imperfections which we have pointed out in a preceding
chapter. It is not easy to understand why mirrors of such
108 TUBULAR REFLECTING STEREOSCOPE. CHAP. VH.
a size should have been adopted. The reason of their being
made of common looking-glass is, that metallic or prismatic
reflectors of such a size would have been extremely expensive.
It is obvious, however, from the slightest consideration,
that reflectors of such a size are wholly unnecessary, and
that one square inch of reflecting surface, in place of thirty-
two, is quite sufficient for uniting the binocular pictures.
We can, therefore, at a price as low as that of the 4-inch
glass reflectors, use mirrors of speculum metal, steel, or even
silver, or rectangular glass prisms, in which the images are
obtained by total reflexion. In this way the stereoscope
becomes a real optical instrument, in which the reflexion is
made from surfaces single and perfectly flat, as in the second
reflexion of the Newtonian telescope and the microscope of
Amici, in which pieces of looking-glass were never used. By
thus diminishing the reflectors, we obtain a portable tubular
instrument occupying nearly as little room as the lenticular
stereoscope, as will be seen from Fig. 28, where abcd is
L B
Fig. 28.
a tube whose diameter is equal to the largest size of one
of the binocular pictures which we propose to use, the left-
eye picture being placed at CD, and the right-eye one at ab.
If they are transparent, they will be illuminated through
paper or ground glass, and if opaque, through openings in
the tube. The image of ab, reflected to the left eye l from
the small mirror mn, and that of CD to the right eye r
CHAP. VTI. SINGLE EEPLECMNG 8TEEB0SCOPE.
109
from the mirror op, will be united exactly as in Mr. Wheat-
stone's instrument already described. The distance of the
two ends, n, p, of the mirrors should be a little greater than
the smallest distance between the two eyes. If we wish to
magnify the picture, we may use two lenses, or substitute
for the reflectors a totally reflecting glass prism, in which
one or two of its surfaces are made convex. 1
2. The Single Reflecting Stereoscope.
This very simple instrument, which, however, answers
only for symmetrical figures, such as those shewn at A and
b, which must be either two right-eye or two left-eye pic-
tures, is shewn in Fig. 29. A single reflector, mn, which
may be either a piece of glass, or a piece of mirror-glass, or a
small metallic speculum, or a rectangular prism, is placed
> We may use also the lens prism, which I proposed many year* ago in the
Edinburgh PhilotophicalJournal.
no
SINGLE REFLECTING STEREOSCOPE. CHAP. VII.
at mn. If we look into it with the left eye l, we see, by
reflexion from its surface at c, a reverted image, or a right-
eye picture of the left-eye picture B, which, when seen in
the direction lca, and combined with the figure a, seen
directly with the right eye R, produces a raised cone ; but
if we turn the reflector i* round, so that the right eye may
look into it, and combine a reverted image of a, with the
figure B seen directly with the left eye l, we shall see a
hollow cone. As bc + cl is greater than ra, the reflected
image will be slightly less in size than the image seen
directly, but the difference is not such as to produce any
perceptible effect upon the appearance of the hollow or the
raised cone. By bringing the picture viewed by reflexion
a little nearer the reflector mn, the two pictures may be
made to have the same apparent magnitude.
If we substitute for the single reflector mn, two reflectors
such as are shewn at m, n, Fig. 30, or a prism p, which
Fig. 30.
gives two internal reflexions, we shall have a general stereo-
scope, which answers for landscapes and portraits.
CHAP. VH. DOUBLE REFLECTING STEREOSCOPE.
Ill
The reflectors m, n or p may be fitted up in a conical tube,
which has an elliptical section to accommodate two figures
at its farther end, the major axis of the ellipse being parallel
to the line joining the two eyes.
3. The Double Reflecting Stereoscope.
This instrument differs from the preceding in having a
single reflector, mn, m'n', for each eye, as shewn in Fig. 31,
and the effect of this is to exhibit, at the same time, the
raised and the hollow cone. The image of b, seen by re-
flexion from mn at the point c, is combined with the picture
of a, seen directly by the right eye R, and forms a hollow
cone ; while the image of a, seen by reflexion from m'n' at
the point c / , is combined with the picture of b, seen directly
by the left eye l, and forms a raised cone.
112
DOUBLE REFLECTING STEREOSCOPE. CHAP. VIL
Another form of the double reflecting stereoscope is shewn
in Fig. 32, which differs from that shewn in Fig. 31 in
Fig. 32.
the position of the two reflectors and of the figures to be
united. The reflecting faces of the mirrors are turned out-
wards, their distance being less than the distance between
the eyes, and the effect of this is to exhibit at the same
time the raised and the hollow cone, the hollow cone being
now on the right-hand side.
If in place of two right or two left eye pictures, as shewn
in Figs. 29, 31, and 32, we use one right eye and one left
eye picture, and combine the reflected image of the one
with the reflected image of the other, we shall have a
raised cone with the stereoscope, shewn in Fig. 31, and a
hollow cone with the one in Fig. 32.
The double reflecting stereoscope, in both its forms, is a
general instrument for portraits and landscapes, and thus
possesses properties peculiar to itself.
CHAP. VIL
TOTAL REFLEXION STEREOSCOPE.
113
The reflectors may be glass or metallic specula, or total
reflexion prisms.
4. The Toted Reflexion Stereoscope.
This form of the stereoscope is a very interesting one,
and possesses valuable properties. It requires only a small
prism and one diagram, or picture of the solid, as seen by
one eye ; the other diagram, or picture which is to be
combined with it, being created by total reflexion from the
base of the prism. This instrument is shewn in Fig. 33,
ij »
where D is the picture of a cone as seen by the left eye l,
and abc a prism, whose base bc is so large, that when the
eye is placed close to it, it may see, by reflexion, the whole
of the diagram d. The angles abc, acb must be equal,
but may be of any magnitude. Great accuracy in the
equality of the angles is not necessary ; and a prism con-
structed, by a lapidary, out of a fragment of thick plate-
114 TOTAL REFLEXION STEREOSCOPE. . CHAP. VII.
glass, the face bc being one of the surfaces of the plate,
will answer the purpose. When the prism is placed at a,
Fig. 34, at one end of a conical tube ld, and the diagram
d at the other end, in a cap, which can be turned round
so as to have the line mn, Fig. 33, which passes through
the centre of the base and summit of the cone parallel to
the line joining the two eyes, the instrument is ready for
use. The observer places his left eye at l, and views with
it the picture D, as seen by total reflexion from the
base bo of the prism, Figs. 33 and 35, while with his
right eye k, Fig. 33, he views the real picture directly.
The first of these pictures being the reverse of the second d,
like all pictures formed by one reflexion, we thus combine
CHAP. VII; TOTAL REFLEXION STEREOSCOPE. 115
two dissimilar pictures into a raised cone, as in the figure,
or into a hollow one, if the picture at d is turned round
180°. If we place the images of two diagrams, one
like one of those at a, Fig. 31, and the other like the
one at b, vertically above one another, we shall then see,
at the same time, the raised and the hollow cone, as pro-
duced in the lenticular stereoscope by the three diagrams,
two like those in Fig. 31, and a third like the one at a.
When the prism is good, the dissimilar image, produced
by the two refractions at b and c, and the one reflexion
at e, is, of course, more accurate than if it had been
drawn by the most skilful artist ; and therefore this
form of the stereoscope has in this respect an advantage
over every other in which two dissimilar figures, executed
by art, are necessary. In consequence of the length of
the reflected pencil db + be + ec + cl being a little
greater than the direct pencil of rays dr, the two images
combined have not exactly the same apparent magnitude ;
but the difference is not perceptible to the eye, and a
remedy could easily be provided were it required.
If the conical tube ld is held in the left hand, the left
eye must be used, and if in the right hand the right eye
must be used, so that the hand may not obstruct the
direct vision of the drawing by the eye which does not
look through the prism. The cone ld must be turned
round slightly in the hand till the line mn joining the
centre and apex of the figure is parallel to the line joining
the two eyes. The same line must be parallel to the plane
of reflexion from the prism ; but this parallelism is secured
by fixing the prism and the drawing.
It is scarcely necessary to state that this stereoscope is
118 SINGLE-PRISM STEREOSCOPE. CHAP. VII.
seen before the rotation of the figure commenced. If
the pyramid had been square, the raised would have
passed into the hollow pyramid by rotations of 45° each.
If it had been rectangular, the change would have been
effected by rotations of 90°. If the space between the
two circular sections of the cone in Fig. 31 had been
uniformly shaded, or if lines had been drawn from every
degree of the one circle to every corresponding degree in
the other, in place of from every 90th degree, as in the
Figure, the raised cone would have gradually diminished
in height, by the rotation of the figure, till it became flat,
after a rotation of 90° ; and by continuing the rotation it
would have become hollow, and gradually reached its maxi-
mum depth after a revolution of 1 80°.
5. The Single-Prism Stereoscope.
Although the idea of uniting the binocular pictures by
a single prism applied to one eye, and refracting one of
the pictures so as to place it upon the other seen directly
by the other eye, or by a prism applied to each eye,
could hardly have escaped the notice of any person study-
ing the subject, yet the experiment was, so far as I
know, first made and published by myself. I found two
prisms quite unnecessary, and therefore abandoned the
use of them, for reasons which will be readily appreciated.
This simple instrument is shewn in Fig. 37, where a, b
are the dissimilar pictures, and p a prism with such a
refracting angle as is sufficient to lay the image of a upon b,
as seen by the right eye. If we place a second prism before
the eye r, we require it only to have half the refracting
angle of the prism p, because each prism now refracts
CHAP. VII.
SINGLE-PRISM STEREOSCOPE.
119
the picture opposite to it only half way between a and B,
where they are united. This, at first sight, appears to be
an advantage, for as there must always be a certain degree
r
Fio. 37.
of colour produced by a single prism, the use of two prisms,
with half the refracting angle, might be supposed to reduce
the colour one-half. But while the colour produced by
each prism is thus reduced, the colour over the whole picture
is the same. Each luminous edge with two prisms has
both red and blue tints, whereas with one prism each lumi-
nous edge has only one colour, either red or blue. If the
picture is very luminous these colours will be seen, but in
many of the finest opaque pictures it is hardly visible. In
order, however, to diminish it, the prism should be made
of glass with the lowest dispersive power, or with rock
crystal. A single plane surface, ground and polished by a
lapidary, upon the edge of a piece of plate glass, a little
120 SINGLE PRISM STEREOSCOPE. CHAP. VH.
larger than the pupil of the eye, will give a prism sufficient
for every ordinary purpose. Any person may make one
in a few minutes for himself, by placing a little bit of
good window glass upon another piece inclined to it at
the proper angle, and inserting in the angle a drop of
fluid. Such a prism will scarcely produce any perceptible
colour.
If a single-prism reflector is to be made perfect, we
have only to make it achromatic, which could be done
extempore, by correcting the colour of the fluid prism
by another fluid prism of different refractive and dispersive
power.
With a good achromatic prism the single-prism stereo-
scope is a very fine instrument ; and no advantage of any
value could be gained by using two achromatic prisms. In
the article on New Stereoscopes, published in the Trans-
actions of the Royal Society of Arts for 1849, and in
the Philosophical Magazine for 1852, I have stated in a
note that / believed that Mr. Wheatstone had used two
achromatic prisms. This, however, was a mistake, as
already explained, 1 for such an instrument was never made,
and has never been named in any work previous to 1849,
when it was mentioned by myself in the note above
referred to.
If we make a double prism, or join two, as shewn at
p, p' in Fig. 38, and apply it to two dissimilar figures
a, b, one of which is the reflected image of the other, so
that with the left eye l and the prism p we place the
refracted image of a upon b, as seen by the right eye b, we
shall see a raised cone, and if with the prism p' we place
1 See Chap. i. pp. 33-36.
CHAP. Vn. OPERA-GLASS STEREOSCOPE. 121
the image of b upon a we shall see a hollow cone. If we
place the left eye l at o, behind the common base of the
\
R
prism, we shall see with one-half of the pupil the hollow
cone and with the other half the raised cone.
6. The Opera-Glass Stereoscope.
As the eyes themselves form a stereoscope to those who
have the power of quickly converging their axes to points
nearer than the object which they contemplate, it might
have been expected that the first attempt to make a
stereoscope for those who do not possess such a power,
would have been to supply them with auxiliary eyeballs
capable of combining binocular pictures of different sizes at
different distances from the eye. This, however, has not
been the case, and the stereoscope for this purpose, which
we are about to describe, is one of the latest of its forms.
In Fig. 39, mn is a small inverting telescope, consisting
of two convex lenses iff, n, placed at the sum of their focal
122
OPERA-GLASS STEREOSCOPE.
CHAP. VII.
distances, and op another of the same kind. When the
two eyes, b, l, look through the two telescopes directly at
the dissimilar pictures a, b, they will see them with perfect
Fig. 39.
distinctness ; but, by the slightest inclination of the axes of
the telescopes, the two images can be combined, and the
stereoscopic effect immediately produced. With the dissi-
milar pictures in the diagram a hollow cone is produced ;
^>
Fio. 40.
but if we look at b with the telescope mV, as in Fig. 40,
and at a' with o'p', a raised cone will be seen. With the
usual binocular slides containing portraits or landscapes, the
CHAP. Vn. EY&GLASS STEREOSCOPE. 123
pictures are seen in relief by combining the right-eye one
with the left-eye one.
The instrument now described is nothing more than a
double opera-glass, which itself forms a good stereoscope.
Owing, however, to the use of a concave eye-glass, the field
of view is very small, and therefore a convex glass, which
gives a larger field, is greatly to be preferred.
The little telescopes, mn, op, may be made one and a half
or even one inch long, and fitted up, either at a fixed or with
a variable inclination, in a pyramidal box, like the lenti-
cular stereoscope, and made equally portable. One of these
instruments was made for me some years ago by Messrs.
Home and Thornthwaite, and I have described it in the
North British Review 1 as having the properties of a Bin-
ocular Cameoscope, and of what has been absurdly called a
Pseudoscope, seeing that every inverting eye-piece and every
stereoscope is entitled to the very same name.
The little telescope may be made of one piece of glass,
convex at each end, or concave at the eye-end if a small field
is not objectionable, — the length of the piece of glass, in
the first case, being equal to the sum, and, in the second
case, to the difference of the focal lengths of the virtual
lenses at each end. 2
7. The Eye-Glass Stethoscope.
As it is impossible to obtain, by the ocular stereoscope,
pictures in relief from the beautiful binocular slides which
are made in every part of the world for the lenticular stereo-
i For 1852, vol. xvii. p. 200.
2 These solid telescopes may be made achromatic by cementing concave lenses
of flint glass upon each end, or of crown glass if they are made of flint glass.
124 EYE-GLASS STEREOSCOPE. CHAP. VII.
scope, it is very desirable to have a portable stereoscope
which can be carried safely in our purse, for the purpose of
examining stereoscopically all such binocular pictures.
If placed together with their plane sides in contact, a
plano-convex lens, ab, and a plano-concave one, cd, of the
same glass and the same focal length, will resemble a thick
watch-glass, and on looking through them, we shall see
objects of their natural size and in their proper place ; but
if we slip the concave lens, cd, to a side, as shewn in Fig. 41,
Fig. 41.
we merely displace the image of the object which we view,
and the displacement increases till the centre of the concave
lens comes to the margin of the convex one. We thus
obtain a variable prism, by means of which we can, with
the left eye, displace one of the binocular pictures, and lay
it upon the other, as seen by the right eye. We may use
semi-lenses or quarters of lenses, and we may make them
achromatic or nearly so if we desire it. Double convex and
double concave lenses may also be used, and the motion of
the concave one regulated by a screw. In one which I con-
stantly use, the concave lens slides in a groove over a convex
quarter lens.
By employing two of these variable prisms, we have an
Universal Stereoscope for uniting pictures of various sizes
and at various distances from each other, and the prisms may
be placed in a pyramidal box, like the lenticular stereoscope.
CHAP. VH. READING-GLA8S STEREOSCOPE. 125
8. The Reading-Gla&s Stereoscope.
If we take a reading-giass whose diameter is not less than
two inches and three quarters, and look through it with
both eyes at a binocular picture in which the right-eye view
is on the left hand, and the left-eye view on the right
hand, as in the ocular stereoscope, we shall see each picture
doubled, and the degree of separation is proportional to the
distance of the picture from the eye. If the distance of the
binocular pictures from each other is small, the two middle
images of the four will be united when their distance from
the lens is not very much greater than its focal length.
With a reading-glass 4 J inches in diameter, with a focal
length of two feet, binocular pictures, in which the distance
of similar parts is nine inches, are united without any exer-
tion of the eyes at the distance of eight feet. With the
same reading-glass, binocular pictures, at the usual distance
of 2J inches, will be united at the distance of 2J or even
2£ feet. If we advance the reading-glass when the distance
is 2 or 3 feet, the picture in relief will be magnified, but,
though the observer may not notice it, the separated images
are now kept united by a slight convergency of the optic"
axes. Although the pictures are placed so far beyond the
anterior focus of the lens, they are exceedingly distinct.
The distinctness of vision is sufficient, at least to long-
sighted eyes, when the pictures are placed within 16 or 18
inches of the observer, that is, 6 or 8 inches nearer the eye
than the anterior focus of the lens. In this case we can
maintain the union of the pictures only when we begin to
view them at a distance of 2 J or 3 feet, and then gradually
advance the lens within 16 or 18 inches of the pictures.
126 CAMERA. STEREOSCOPE. CHAP. VH.
At considerable distances, the pictures are most magnified
by advancing the lens while the head of the observer is
stationary.
9. The Camera Stereoscope.
The object of this instrument is to unite the transient
pictures of groups of persons or landscapes, as delineated
in two dissimilar pictures, on the ground glass of a bin-
ocular camera. If we attach to the back of the camera a
lenticular stereoscope, so that the two pictures on the ground
glass occupy the same place as its usual binocular slides,
we shall see the group of figures in relief under every change
of attitude, position, and expression. The two pictures may
be formed in the air, or, more curiously still, upon a wreath
of smoke. As the figures are necessarily inverted in the
camera, they will remain inverted by the lenticular and
every other instrument but the opera-glass stereoscope,
which inverts the object By applying it therefore to the
camera, we obtain an instrument by which the photographic
artist can make experiments, and try the effect which will
be produced by his pictures before he takes them. He
can thus select the best forms of groups of persons and
of landscapes, and thus produce works of great interest
and value.
10. The Chromatic Stereoscope.
The chromatic stereoscope is a form of the instrument in
which relief or apparent solidity is given to a single figure
with different colours delineated upon a plane surface.
If we look with both eyes through a lens l l, Fig. 42,
about 2 J inches in diameter or upwards, at any object having
CHAP. vn.
CHROMATIC STEREOSCOPK
127
colours of different degrees of refrangibility, such as the
coloured boundary lines on a map, a red rose among green
leaves and on a blue background, or any scarlet object what-
Fio. 42.
ever upon a violet ground, or in general any two simple colours
not of the same degree of refrangibility, the differently
coloured parts of tike object will appear at different distances
from the observer.
Let us suppose the rays to be red and violet, those which
differ most in refrangibility. If the red rays radiate from
the anterior focus b, or red rays of the lens l i^ they will
emerge parallel, and enter the eye at m ; but the violet rays
radiating from the same focus, being more refrangible, will
emerge in a state of convergence, as shewn at mv y nv, the
red rays being mr, nr. The part of the object, therefore,
from which the red rays come, will appear nearer to the
observer than the parts from which the violet rays come,
and if there are other colours or rays of intermediate re-
frangibilities, they will appear to come from intermediate
distances.
128 CHROMATIC STEREOSCOPE. CHAP. VII.
If we place a small red and violet disc, like the smallest
wafer, beside one another, so that the line joining their
centres is perpendicular to the line joining the eyes, and
suppose that rays from both enter the eyes with their opti-
cal axes parallel, it is obvious that the distance between the
violet images on each retina will be less than the distance
between the red images, and consequently the eyes will re-
quire to converge their axes to a nearer point in order to
unite the red images, than in order to unite the violet
images. The red images will therefore appear at this nearer
point of convergence, just as, in the lenticular stereoscope,
the more distant pair of points in the dissimilar images
appear when united nearer to the eye. By the two eyes
alone, therefore, we obtain a certain, though a small degree
of relief from colours. With the lens ll, however, the
effect is greatly increased, and we have the sum of the two
effects.
From these observations, it is manifest that the reverse
effect must be produced by a concave lens, or by the com-
mon stereoscope, when two coloured objects are employed
or united. The bine part of the object will be seen nearer
the observer, and the red part of it more remote. It is,
however, a curious fact, and one which appeared difficult to
explain, that in the stereoscope the colour-relief was not
brought out as might have been expected. Sometimes the
xed was nearest the eye, and sometimes the blue, and some-
times the object appeared without any relief. The cause of
this is, that the colour-relief given by the common stereo-
scope was the opposite of that given by the eye, and it was
only the difference of these effects that ought to have been
observed ; and though the influence of the eyes was an
CHAP. VIL MICROSCOPE STEREOSCOPE. 129
inferior one, it often acted alone, and sometimes ceased to
act at all, in virtue of that property of vision by which we
see only with one eye when we are looking with two.
In the chromatic stereoscope, Fig. 42, the intermediate
part mn of the lens is of no use, so that out of the margin of
a lens upwards of 2 J inches in diameter, we may cut a dozen
of portions capable of making as many instruments. These
portions, however, a little larger only than the pupil of the
eye, must be placed in the same position as in Fig. 42.
All the effects which we have described are greatly in-
creased by using lenses of highly-dispersing flint glass, oil
of cassia, and other fluids of a great dispersive power, and
avoiding the use of compound colours in the objects placed
in the stereoscope.
It is an obvious result of these observations, that in
painting, and in coloured decorations of all kinds, the red
or less refrangible colours should be given to the prominent
parts of the object to be represented, and the blue or more
refrangible colours to the background and the parts of the
objects that are to retire from the eye.
11. The Microscope Stereoscope.
The lenticular form of the stereoscope is admirably fitted
for its application to small and microscopic objects. The
first instruments of this kind were constructed by myself
with quarter-inch lenses, and were 3 inches long and only
1 and 1 \ deep. 1 They may be carried in the pocket, and
exhibit all the properties of the instrument to the greatest
advantage. The mode of constructing and using the instru-
ment is precisely the same as in the common stereoscope ;
i Phil Mag., Jan. 1852, vol. iii. p. 19.
I
130 MICE08COPE STEREOSCOPE. CHAP. TIL
but in taking the dissimilar pictures, we must use either a
small binocular camera, which will give considerably mag-
nified representations of the objects, or we must procure them
from the compound microscope. The pictures may be ob-
tained with a small single camera, by first taking one pic-
ture, and then shifting the object in the focus of the lens,
through a space corresponding with the binocular angle. To
find this space, which we may call x, make d the distance
of the object from the lens, n the number of times it is
to be magnified, or the distance of the image behind the
lens, and d the distance of the eyes ; then we shall have
nd :d = i> :x, and x =-,
that is, the space is equal to the distance between the eyes
divided by the magnifying power.
With the binocular microscope of Professor Riddell, 1 and
the same instrument as improved by M. Nachet, binocular
pictures are obtained directly by having them drawn, as
Professor Riddell suggests, by the camera lucida, but it
would be preferable to take them photographically.
Portraits for lockets or rings might be put into a very
small stereoscope, by folding the one lens back upon the
other.
1 American Journal of Science, 1852, vol xt. p. 68.
CHAP. VHI. METHOD OF TAKING THE PICTURES. 131
CHAPTER VIII
METHOD OP TAKING PICTUBES FOR THE STEREOSCOPE.
However perfect be the stereoscope which we employ,
the effect which it produces depends upon the accuracy
with which the binocular pictures are prepared. The
pictures required for the stereoscope may be arranged in
four classes : —
1. The representations of geometrical solids as seen with
two eyes.
2. Portraits, or groups of portraits, taken from living
persons or animals.
3. Landscapes, buildings, and machines or instruments.
4. Solids of all kinds, the productions of nature or of
art.
Geometrical Solids.
Representations of geometrical solids, were, as we have
already seen, the only objects which for many years were
employed in the reflecting stereoscope. The figures thus
used are so well known that it is unnecessary to devote
much space to their consideration. For ordinary purposes
they may be drawn by the hand, and composed of squares,
rectangles, and circles, representing quadrangular pyramids,
truncated, or terminating in a point, cones, pyramids with
polygonal bases, or more complex forms in which raised
132
METHOD OF TAKING THE P1CTUSXS. CHAP. VTTJ.
pyramids or cones rise out of quadrangular or conical hol-
lows. All these figures may be drawn by the hand, and
will produce solid forms sufficiently striking to illustrate
the properties of the stereoscope, though not accurate repre-
sentations of any actual solid seen by binocular vision.
If one of the binocular pictures is not equal to the other
in its base or summit, and if the lines of the one are made
crooked, it is curious to observe how the appearance of the
resulting solid is still maintained and varied.
The following method of drawing upon a plane the dis-
similar representations of solids, will give results in the
stereoscope that are perfectly correct : —
-- N
Let l, b, Fig. 43, be the left and right eye, and a the
middle point between them. Let mn be the plane on
CHAP. VIE METHOD OF TAKING THE FXCTUBES. 133
which an object or solid whose height is cb is to be drawn.
Through B draw lb, meeting hk in c ; then if the object
is a solid, with its apex at b, cc will be the distance of its
apex from the centre o of its base, as seen by the left eye.
When seen by the right eye b, cd will be its distance, c'
lying on the left side of c. Hence if the figure is a cone,
the dissimilar pictures of it will be two circles, in one of
which its apex is placed at the distance cc from its centre,
and in the other at the distance cc' on the other side of the
centre. When these two plane figures are placed in the
stereoscope, they will, when combined, represent a raised
cone when the points c, c' are nearer one another than the
centres of the circles representing the cone's base, and a
hollow cone when the figures are interchanged.
If we call E the distance between the two eyes, and
h the height of the solid, we shall have ab : h = y : cc,
^ cc = jrr& or iTP vhich. ™& # ve va ^ e result 8 m
the following table, E being 2£, and AC 8 inches : —
Height of object.
BC = A AB = AC — k CC
Inches
1 7 0.179
2 6 0.4166
3 6 0.75
4 4 1.25
5 3 2.083
6 2 3.75
7 1 8.76
8 Infinite.
If we now converge the optic axes to a point 6, and
wish to ascertain the value of cc, which will give dif-
134 METHOD OP TAKING THE PICTURES. CHAP. Vm,
ferent depths, d, of the hollow solids corresponding to
different values of c6, we snail have a 6 : | = d : c<? 9 and
cc ' = 5T& w ^ c ^> niaking a o= 8 inches, as before, will
give the following results : —
Depth.
0b = d
Ab=AO + d
Inches.
1
9
0.189
2
10
0.26
3
11
0.34
4
12
0.4166
6
18
0.48
6
14
0.636
7
16
0.68
8
16
0.626
9
17
0.663
10
18
0.696
11
19
0.723
12
20
0.76
The values of h and d when cc, cc' are known, will be
found from the formulae h = ^^, and d = 2AB E °«' .
As cc is always equal to cc' in each pair of figures or dis-
similar pictures, the depth of the hollow cone will always
appear much greater than the height of the raised one.
When cc = c<f = 0-75, hid = 3:12. When cc = cd
= 04166, h : d = 2 : 4, and when cc = cc? = 0-139,
h:d = 0-8:1-0.
When the solids of which we wish to have binocular
pictures are symmetrical, the one picture is the reflected
image of the other, or its reverse, so that when we have
drawn the solid as seen by one eye, we may obtain the other
CHAP. Vm. METHOD OF TAKING THE PICTURES. 135
by copying its reflected image, or by simply taking a copy
of it as seen through the paper.
When the geometrical solids are not symmetrical, their dis-
similar pictures must be taken photographically from models,
in the same manner as the dissimilar pictures of other solids.
Portraits of Living Persons or Animals.
Although it is possible for a clever artist to take two
portraits, the one as seen by his right, and the other as seen
by his left eye, yet, owing to the impossibility of fixing the
sitter, it would be a very difficult task. A bust or statue
would be more easily taken by fixing two apertures 2 \ inches
distant, as the two points of sight, but even in this case
the result would be imperfect. The photographic camera
is the only means by which living persons and statues can
be represented by means of two plane pictures to be combined
by the stereoscope ; and but for the art of photography, this
instrument would have had a very limited application.
It is generally supposed that photographic pictures,
whether in Daguerreotype or Talbotype, are accurate repre-
sentations of the human face and form, when the sitter sits
steadily, and the artist knows the resources of his art. Quis
solem essefalsum dicere audeat ? says the photographer, in
rapture with his art. Solem essefalsum dicere audeo, re-
plies the man of science, in reference to the hideous repre-
sentations of humanity which proceed from the studio of
the photographer. The sun never errs in the part which
he has to perform. The sitter may sometimes contribute
his share to the hideousness of his portrait by involuntary
nervous motion, but it is upon the artist or his art that the
blame must be laid.
136 A CAMERA WITHOUT LENSES. CHAP. Vm.
If the single portrait of an individual is a misrepresenta-
tion of his form and expression, the combination of two such
pictures into a solid must be more hideous still, not merely
because the error in form and expression is retained or
doubled, but because the source of error in the single por-
trait is incompatible with the application of the stereoscopic
principle in giving relief to the plane pictures. The art of
stereoscopic portraiture is in its infancy, and we shall there-
fore devote some space to the development of its true prin-
ciples and practice.
In treating of the images of objects formed by lenses and
mirrors with spherical surfaces, optical writers have satisfied
themselves by shewing that the images of straight lines so
formed are conic sections, elliptical, parabolic, or hyperbolic.
I am not aware that any writer has treated of the images of
solid bodies, and of their shape as affected by the size of the
lenses or mirrors by which they are formed, or has even
attempted to shew how a perfect image of any object can
be obtained. We shall endeavour to supply this defect.
In a previous chapter we have explained the manner in
which images are formed by a small aperture, h, in the side,
mn, of a camera, or in the window-shutter of a dark room.
The rectangles br, 6V, and 6V, are images of the object
eb, according as they are received at the same distance
from the lens as the object, or at a less or a greater distance,
the size of the image being to that of the object as their
respective distances from the hole h. Pictures thus taken
are accurate representations of the object, whether it be
lineal, superficial, or solid, as seen from or through the hole
h ; and if we could throw sufficient light upon the object,
or make the material which receives the image very sensi-
CHAP. Vm. CAMERA WITH A SMALL SINGLE LENS.
137
tive, we should require no other camera for giving us photo-
graphs of all sizes. The only source of error which we can
conceive, is that which may arise from the inflexion of light,
Fig. 44.
but we believe that it would exercise a small influence, if
any, and it is only by experiment that its effect can be
ascertained.
The Rev. Mr. Egerton and I have obtained photographs
of a bust, in the course of ten minutes, with a very faint sun,
and through an aperture less than the hundredth of an inch ;
and I have no doubt that when chemistry has furnished us
with a material more sensitive to light, a camera without
lenses, and with only a pin-hole, will be the favourite in-
strument of the photographer. At present, no sitter could
preserve his composure and expression during the number
of minutes which are required to complete the picture.
But though we cannot use this theoretical camera, we
may make some approximation to it. If we make the hole
H a quarter of an inch, the pictures br> &c., will be faint
and indistinct ; but by placing a thin lens a quarter of an
138 EKBOBS OF THE COMMON CAMERA. CHAP. Vm.
inch in diameter in the hole h, the distinctness of the pic-
ture will be restored, and, from the introduction of so much
light, the photograph may be completed in a sufficiently
short time. The lens should be made of rock crystal, which
has a small dispersive power, and the ratio of curvature of its
surfaces should be as six to one, the flattest side being turned
to the picture. In this way there will be very little colour
and spherical aberration, and no error produced by any striae
or want of homogeneity in the glass.
As the hole h is nearly the same as the greatest opening
of the pupil, the picture which is formed by the enclosed
lens will be almost identical with the one we see in mono-
cular vision, which is always the most perfect representation
of figures in relief.
With this approximately perfect camera, let us now com-
pare the expensive and magnificent instruments with which
the photographer practises his art. We shall suppose his
camera to have its lens or lenses with an aperture of only three
inches, as shewn at l e in Fig. 45. If we cover the whole
Fid. 45.
lens, or reduce its aperture to a quarter of an inch, as shewn
at a, we shall have a correct picture of the sitter. Let us
now take other four pictures of the same person, by re-
CHAP. Vm. ERRORS FROM LARGE LENSES. 139
moving the aperture successively to b, c, d, and e : It is
obvious that these pictures will all differ very perceptibly
from each other. In the picture obtained through d, we
shall see parts on the left side of the head which are not
seen in the picture through c, and in the one through c,
parts on the right side of the head not seen through d. In
short, the pictures obtained through c and d are accurate
dissimilar pictures, such as we have in binocular vision, (the
distance cd being 2 J inches,) and fitted for the stereoscope.
In like manner, the pictures through b and e will be different
from the preceding, and different from one another. In the
one through 6, we shall see parts below the eyebrows, below
the nose, below the upper lip, and below the chin, which
are not visible in the picture through e, nor in those through
c and d ; while in the picture through e, we shall see parts
above the brow, and above the upper lip, &c, which are not
seen in the pictures through b, c, and d. In whatever part
of the lens, lb, we place the aperture, we obtain a picture
different from that through any other part, and therefore it
follows, that with a lens whose aperture is three inches, the
photographic picture is a combination of about one hundred
and thirty dissimilar pictures of the sitter, the similar parts
of which are net coincident ; or to express it in the lan-
guage of perspective, the picture is a combination of about
one hundred and thirty pictures of the sitter, taken from one
hundred and thirty different points of sight ! If such is the
picture formed by a three-inch lens, what must be the
amount of the anamorphism, or distortion of form, which is
produced by photographic lenses of diameters from three to
twelve inches, actually used in photography I 1
1 See my Treatise on Optics, 2d edit, chap. rli. p. 65.
140 ESBOBS FROM LAEGE LENSES. CHAP. Yin.
But it is not merely by the size of the lenses that hideous
portraits are produced. In cameras with two achromatic
lenses, the rays which form the picture pass through a large
thickness of glass, which may not be altogether homoge-
neous, — through eight surfaces which may not be truly
spherical, and which certainly scatter light in all directions, —
and through an optical combination in which straight lines
in the object must be conic sections in the picture !
Photography, therefore, cannot even approximate to per-
fection till the artist works with a camera furnished with a
single quarter of an inch lens of rock crystal, having its
radii of curvature as six to one, or what experience may find
better, with an achromatic lens of the same aperture. And
we may state with equal confidence, that the photographer
who has the sagacity to perceive the defects of his instru-
ments, the honesty to avow it, and the skill to remedy them
by the applications of modern science, will take a place as
high in photographic portraiture as a Reynolds or a Law-
rence in the sister art.
Such being the nature of single portraits, we may form
some notion of the effect produced by combining dissimilar
ones in the stereoscope, so as to represent the original in
relief. The single pictures themselves, including binocular
and multocular representations of the individual, must, when
combined, exhibit a very imperfect portrait in relief — so
imperfect, indeed, that the artist is obliged to take his two
pictures from points of sight different from the correct
points, in order to produce the least disagreeable result.
This will appear after we have explained the correct method
of taking binocular portraits for the stereoscope.
No person but a painter, or one who has the eye and the
CHAP. Vm. METHOD OF TAKING THE PICTUBES. 141
taste of a painter, is qualified to be a photographer either
in single or binocular portraiture. The first step in taking
a portrait or copying a statue, is to ascertain in what aspect
and at what distance from the eye it ought to be taken.
In order to understand this subject, we shall first con-
sider the vision, with one eye, of objects of three dimensions,
when of different magnitudes and placed at different dis-
tances. When we thus view a building, or a full-length or
colossal statue, at a short distance, a picture of all its visible
parts is formed on the retina. If we view it at a greater
distance, certain parts cease to be seen, and other parts
come into view ; and this change in the picture will go on,
but will become less and less perceptible as we retire from
the original If we now look at the building or statue from
a distance through a telescope, so as to present it to us
with the same distinctness, and of the same apparent mag-
nitude as we saw it at our first position, the two pictures
will be essentially different ; all the parts which ceased to
be visible as we retired will still be invisible, and all the
parts which were not seen at our first position, but became
visible by retiring, will be seen in the telescopic picture.
Hence the parts seen by the near eye, and not by the distant
telescope, will be those towards the middle of the building
or statue, whose surfaces converge, as it were, towards the
eye; while those seen by the telescope, and not by the
eye, will be the external parts of the object, whose sur-
faces converge less, or approach to parallelism. It will
depend on the nature of the building or the statue which
of these pictures gives us the most favourable representation
of it.
If we now suppose the building or statue to be reduced
142 METHOD OP TAKING THE PICTURES. CHAP. VJ1I.
in the most perfect manner, — to half its size, for example, —
then it is obvious that these two perfectly similar solids will
afford a different picture, whether viewed by the eye or by
the telescope. In the reduced copy, the inner surfaces
visible in the original will disappear, and the outer surfaces
become visible; and, as formerly, it will depend on the
nature of the building or the statue whether the reduced or
the original copy gives the best picture.
If we repeat the preceding experiments with two eyes
in place of one 9 the building or statue will have a different
appearance ; surfaces and parts, formerly invisible, will
become visible, and the body will be better seen because
we see more of it ; but then the parts thus brought into
view being seen, generally speaking, with one eye, will have
less brightness than the rest of the picture. But though
we see more of the body in binocular vision, it is only parts
of vertical surfaces perpendicular to the line joining the
eyes that are thus brought into view, the parts of similar
horizontal surfaces remaining invisible as with one eye. It
would require a pair of eyes placed vertically, that is, with
the line joining them in a vertical direction, to enable us
to see the horizontal as well as the vertical surfaces ; and
it would require a pair of eyes inclined at all possible
angles, that is, a ring of eyes 2£ inches in diameter, to
enable us to have a perfectly symmetrical view of the
statue.
These observations will enable us to answer the question,
whether or not a reduced copy of a statue, of precisely the
same form in all its parts, will give us, either by monocular
or binocular vision, a better view of it as a work of art.
As it is the outer parts or surfaces of a large statue that
CHAP. Vm. PROPER POSITION OF THE SITTER. 143
are invisible, its great outline and largest parts must be
best seen in the reduced copy ; and consequently its relief,
or third dimension in space, must be much greater in the
reduced copy. This will be better understood if we suppose
a sphere to be substituted for the statue. If the sphere
exceeds in diameter the distance between the pupils of the
right and left eye, or 2\ inches, we shall not see a complete
hemisphere, unless from an infinite distance. If the sphere
is very much larger, we shall see only a segment, whose relief,
in place of being equal to the radius of the sphere, is equal
only to the versed sine of half the visible segment. Hence
it is obvious that a reduced copy of a statue is not only
better seen from more of its parts being visible, but is also
seen in stronger relief.
On the Proper Position of the Sitter.
With these observations we are now prepared to explain
the proper method of taking binocular portraits for the
stereoscope.
The first and most important step is to fix upon the
position of the sitter, — to select the best aspect of the face,
and, what is of more importance than is generally sup-
posed, to determine the best distance from the camera at
which he should be placed. At a short distance certain
parts of one face and figure which should be seen are
concealed, and certain parts of other faces are concealed
which should be seen. Prominent ears may be either
hid or made less prominent by diminishing the distance,
and if the sight of both ears is desirable the distance
should be increased. Prominent features become less pro-
minent by distance, and their influence in the picture is
144 PROPER POSITION OP THE SITTER. CHAP. Vm.
also diminished by the increased vision which distance
gives of the round of the head. The outline of the face
and head varies essentially with the distance, and hence it
is of great importance to choose the best A long and
narrow face requires to be viewed at a different distance
from one that is short and round. Articles of dress even
may have a better or a worse appearance according to the
distance at which we see them.
Let us now suppose the proper distance to be six feet,
and since it is impossible to give any rules for taking
binocular portraits with large lenses we must assume a
standard camera with a lens a quarter of an inch in
diameter, as the only one which can give a correct picture
as seen with one eye. If the portrait is wanted for a ring,
a locket, or a binocular slide, its size is determined by its
purpose, and the photographer must have a camera (which
he has not) to produce these different pictures. His own
camera will, no doubt, take a picture for a ring, a locket,
or a binocular slide, but he does this by placing the sitter
at different distances, — at a very great distance for the
ring picture, at a considerable distance for the locket
picture, and at a shorter distance for the binocular one ;
but none of these distances are the distance which has been
selected as the proper one. With a single lens camera,
however, he requires only several quarter-inch lenses of
different focal lengths to obtain the portrait of the sitter
when placed at the proper distance from the camera.
In order to take binocular portraits for the stereoscope a
binocular camera is required, having its lenses of such a
focal length as to produce two equal pictures of the same
object and of the proper size. Those in general use for
CHAP. Vm. BINOCULAR CAMERA. 145
th6 lenticular stereoscope vary from 2-1 inches to 2*3
in breadth, and from 2-5 inches to 2-8 in height, the dis-
tance between similar points in the two pictures varying
from 2-30 inches to 2*57, according to the different dis-
tances of the foreground and the remotest object in the
picture.
Having fixed upon the proper distance of the sitter,
which we shall suppose to be six feet, — a distance very suit-
able for examining a bust or a picture, we have now to
take two portraits of him, which, when placed in the
stereoscope, shall have the same relief and the same
appearance as the sitter when viewed from the distance of
six feet. This will be best done by a binocular camera,
which we shall now describe.
The Binocular Camera.
This instrument differs from the common camera in
having two lenses with the same aperture and focal
length, for taking at the same instant the picture of the
sitter as seen at the distance of six feet, or any other dis-
tance. As it is impossible to grind and polish two lenses,
whether single or achromatic, of exactly the same focal
length, even when we have the same glass for both, we
must bisect a good lens, and use the two semi-lenses,
ground into a circular form, in order to obtain pictures of
exactly the same size and definition. These lenses should
be placed with their diameters of bisection parallel to one
another, and perpendicular to the horizon, at the distance of
2£ inches, as shewn in Fig. 45, where mn is the camera, L,
l' the two lenses, placed in two Bhort tubes, so that by the
usual mechanical means they can be directed to the sitter,
K
146 BOTOCULAB CAMERA. CHAP. VIII.
or have their axes converged upon him, as shewn in the
Figure, where ab is the sitter, a 6 his image as given by
the lens l, and d If as given by the lens l'. These pictures
Fig. 45.
are obviously the very same that would be seen by the artist
with his two eyes at l and l', and asALB = «L& = a! lib', the
pictures will have the same apparent magnitude as the
original, and will in no respect differ from it as seen by each
eye from k, tf, e« being equal to aL, and tfa! to ah.
Since the publication in 1849 of my description of the
binocular camera, a similar instrument was proposed in
Paris by a photographer, M. Quinet, who gave it the name
of Quinetoscope, which, as the Abbs' Moigno observes,
means an instrument for seeing M. Quinet ! I have not
seen this camera, but, from the following notice of it by the
Abbe 4 Moigno, it does not appear to be different from
mine : — " Nous avons £te* a la fois surpris et tres-satisfait
de retrouver dans le Quinetoscope la chambre binoculaire de
notre ami Sir David BrewBter, telle que nous l'avons
d&rite apres lui il y a dix-huit mois dans notre brochure
CHAP. VIE. BINOCULAR CAMERA. 147
intitule Stereoscope" Continuing to Bpeak of M. Quinet's
camera, the Abbe' is led to criticise unjustly what he calls
the limitation of the instrument : — " En un mot, ce
charmant appareil est aussi bien construit qu'il peut etre,
et nous d&irons ardemment qu'il se repand assez pour
recompenser M. Quinet de son habiletd et de ses peines.
Employe* dans les limites fixees a l'avance par son veritable
inventeur> Sir David Brewster ; c'est-a-dire, employe' a
reproduire des objeU de petite et moyenne grandeur, il
donnera assez beaux resultats. II ne pourra pas servir,
evidemment, il ne donnera pas bien Veffet stereoscopique
voulu, quand on voudra Vappliquer a de trfa-grands objets,
on a des vues ou paysages pris oVune trls-grande distance ;
maw il est de la nature des osuvres humaines d'etre essen-
tiellement bornees" 1 This criticism on the limitation of the
camera is wholly incorrect ; and it will be made apparent,
in a future part of the Chapter, that for objects of all sizes
and at all distances the binocular camera gives the very
representations which we see, and that other methods,
referred to as superior, give unreal and untruthful pictures,
for the purpose of producing a startling relief.
In stating, as he subsequently does, that the angles at
which the pictures should be taken " are too vaguely
indicated by theory," 2 the Abbe* cannot have appealed to
his own optical knowledge, but must have trusted to the
practice of Mr. Claudet, who asserts " that there cannot
be any rule for fixing the binocular angle of camera
obscuras. It is a matter of taste and artistic illusion." 8
No question of science can be a matter of taste, and no
i See Cosmos, vol. ii. pp. 622, 624. » Id. vol vii. p. 494.
* Id. vol iii. p. 658.
148
BINOCULAR CAMERA.
chap. vm.
illusion can be artistic which is a misrepresentation of
nature.
When the artist has not a binocular camera he must
place his single camera successively in such positions that
the axis of his lens may have the directions el, el' making
an angle equal to lcl', the angle which the distance between
the eyes subtends at the distance of the sitter from the
lenses. This angle is found by the following formula : —
Tang. £A = i? = >|£
d being the distance between the eyes, d the distance of the
sitter, and a the angle which the distance between the eyes,
= 2*5, subtends at the distance of the sitter. These angles
for different distances are given in the following table : —
D = Distance of Camera
A
= Angle formed by tbe two
from the Sitter. directions of tbe Camera.
5 inches, ... 28° 6'
6,
23 32
7,
20 14
8,
17 46
9,
15 48
10,
14 15
11,
13
12, 1 foot,
11 54
13,
11
14,
10 17
15,
9 32
16,
8 56
n,
8 24
18,
7 56
19,
7 31
20,
7 10
24, 2 feet,
5 58
30,
4 46
CHAP. Vm. RULE FOR BINOCULAS
L PICTURES.
D=Di*aaee of Camera, A
= Angle formed by the
from the Sitter.
directions of the Camei
36 inches, 3 feet, .
3° 59'
42,
3 25
48, 4 feet,
2 59
54,
2 39
60, 5 feet,
2 23
72, 6 feet,
1 59
84, 7 feet,
1 42
96, 8 feet,
1 30
108, 9 feet,
1 20
120, 10 feet,
1 12
149
The numbers given in the greater part of the preceding
table can be of use only when we wish to take binocular
pictures of small objects placed at short distances from
cameras of a diminutive size. In photographic portraiture
they are of no use. The correct angle for a distance of six
feet must not exceed two degrees, — for a distance of eight
feet, one and a half degrees, and for a distance of ten feet,
one and a fifth degree. Mr. Wheatstone has given quite a
different rule. He makes the angle to depend, not on the
distance of the sitter from the camera, but on the distance
of the binocular picture in the stereoscope from the eyes of
the observer ! According to the rule which I have demon-
strated, the angle of convergency for a distance of six feet
must be 1° 59', whereas in a stereoscope of any kind, with
the pictures six inches from the eyes, Mr. Wheatstone makes
it 23° 32' ! As such a difference is a scandal to science,
we must endeavour to place the subject in its true light,
and it will be interesting to observe how the problem has
been dealt with by the professional photographer. The fol-
lowing is Mr. Wheatstone's explanation of his own rule, or
rather his mode of stating it : —
150 RULE FOR BINOCULAR PICTURES. CHAP. Vm.
" With respect," says he, " to the means of preparing
the binocular photographs, (and in this term I include both
Talbotypes and Daguerreotypes,) little requires to be said
beyond a few directions as to the proper positions in which
it is necessary to place the camera in order to obtain the
two required projections.
" We will suppose that the binocular pictures are required
to be seen in the stereoscope at a distance of eight inches
before the eyes, in which case the convergence of the optic
axes is about 1 8°. To obtain the proper projections for this
distance, the camera must be placed with its lens accurately
directed towards the object successively in two points of the
circumference of a circle, of which the object is the centre,
and the points at which the camera is so placed must have
the angular distance of 1 8° from each other, exactly that of
the optic axes in the stereoscope. The distance of the
camera from the object may be taken arbitrarily, for so
long as the same angle is employed, whatever that distance
may be, the picture will exhibit in the stereoscope the same
relief, and be seen at the same distance of eight inches,
only the magnitude of the picture will appear different.
Miniature stereoscopic representations of buildings and full-
sized statues are, therefore, obtained merely by taking the
two projections of the object from a considerable distance,
but at the same time as if the object were only eight inches
distant, that is, at an angle of 18 ." 1
Such is Mr. Wheatstone's rule, for which he has assigned
no reason whatever. In describing the binocular camera,
in which the lenses must be only 2 J inches distant for por-
traits, I have shewn that the pictures which it gives are
i Phil Trans., 1852, p. 7.
CHAP. VHI. RULE FOR BINOCULAR PICTURES. 151
perfect representations of the original, and therefore pictures
taken with lenses or cameras at any other distance, must be
different from those which are seen by the artist looking at
the sitter from his camera. They are, doubtless, both pic-
tures of the sitter, but the picture taken by Mr. Wheat-
stone's rule is one which no man ever saw or can see, until
he can place his eyes at the distance of twenty inches I It
is, in short, the picture of a living doll, in which parts are
seen which are never seen in society, and parts hid which
are always seen.
In order to throw some light upon his views, Mr. Wheat-
Btone got " a number of Daguerreotypes of the same bust
taken at a variety of different angles, so that he was enabled
to place in the stereoscope two pictures taken at any angular
distance from 2° to 18°, the former corresponding to a dis-
tance of about six feet, and the latter to a distance of
about eight inches." In those taken at 2°, (the proper
angle,) there is " an undue elongation of lines joining two
unequally distant points, so that all the features of a bust
appear to be exaggerated in depth ;" while in those taken
at 1 8°, " there is an undue shortening of the same lines,
so that the appearance of a bas-relief is obtained from the
two projections of the bust, the apparent dimensions in
breadth and height remaining in both cases the same."
Although Mr. Wheatstone speaks thus decidedly of the
relative effect produced by combining pictures taken at 2£°
and 18°, yet in the very next paragraph he makes state-
ments entirely incompatible with his previous observations.
" When the optic axes," he says, " are parallel, in strictness
there should be no difference between the pictures presented
to each eye, and in this case there would be no binocular
152 ERRONEOUS METHODS CONSIDERED. CHAP. Vm.
relief, but I find iliat an excellent effect is produced when
the axes are nearly parallel, by pictures taken at an incli-
nation of 7° or 8°, and even a difference of 16° or 17° has
no decidedly bad effect /"
That Mr. Wheatstone observed all these contradictory
facts we do not doubt, but why he observed them, and
what was their cause, is a question of scientific as well as
of practical importance. Mr. Wheatstone was not aware 1
that the Daguerreotype pictures which he was combining,
taken with large lenses, were not pictures as seen with two
human eyes, but were actually binocular and multocular
monstrosities, entirely unfit for the experiments he was
carrying on, and therefore incapable of testing the only true
method of taking binocular pictures which we have already
explained.
Had Mr. Wheatstone combined pictures, each of which
was a correct monocular picture, as seen with each eye, and
as taken with a small aperture or a small lens, he would
have found no discrepancy between the results of observa-
tion and of science. From the same cause, we presume,
namely, the use of multocular pictures, Mr. Alfred Smee 2
has been led to a singular method of taking binocular ones.
In one place he implicitly adopts Mr. Wheatstone's erro-
neous rule. " The pictures for the stereoscope," he says,
" are taken at two stations, at a greater or less distance
apart, according to the distance at which they are to be
viewed. For a distance of 8 inches the two pictures are
taken at angles of 18°, for 13 inches 10°, for 18 inches
1 Mr. Wheatstone's paper was published before I had pointed oat the deformities
produced by large lenses. See p. 130.
* The Eye in Health and Disease, by Alfred Smee, 2d edit. 1854, pp. 85-95.
CHAP. Vm. MR. ALFRED SMEE'S METHOD. 153
8°, and for 4 feet 4°." But when he comes to describe
his own method he seems to know and to follow the true
method, if we rightly understand his meaning. " To
obtain a binocular picture of anybody," he says, "the
camera must be employed to take half the impression, and
then it must be moved in the arc of a circle of which the
distance from the camera to the point of sight 1 is the
radius for about 2£ inches when a second picture is taken,
and the two impressions conjointly form one binocular
picture. There are many ways by which this result may
be obtained. A spot may be placed on the ground-glass
on which the point of sight should be made exactly to fall.
The camera may then be moved 2^ inches, and adjusted
till the point of sight falls again upon the same spot on
the ground-glass, when, if the camera has been moved in a
true horizontal plane the effect of the double picture will be
perfect," This is precisely the true method of taking
binocular pictures which we had given long before, but it
is true only when small lenses are used. In order to
obtain this motion in the true arc of a circle the camera
was moved on two cones which converged to the point of
sight, and Mr. Smee thus obtained pictures of the usual
character. But in making these experiments he was led to
take pictures when the camera was in continual motion
backwards and forwards for 2\ inches, and he remarks
that " in this case the picture was even more beautiful
than when the two images were superimposed /" " This
experiment," he adds, " is very remarkable, for who would
have thought formerly that a picture could possibly have
1 This expression has a different meaning in perspective. We understand it to
mean here the point of the sitter or object, which is to be the centre of the picture.
154 MR. ALFRED SMEE'S METHOD. CHAP. Vm.
been made with a camera in continual motion ? Neverthe-
less we accomplish it every day with ease, and the character
of the likeness is wonderfully improved by it." We have
now left the regions of science, and have to abjudicate on
a matter of opinion and taste. Mr. Smee has been so kind
as to send me a picture thus taken. It is a good photo-
graph with features enlarged in all azimuths, but it has
no other relief than that which we have described as
monocular.
A singular effect of combining pictures taken at extreme
angles has been noticed by Admiral Lageol. Having taken
the portrait of one of his friends when his eyes were
directed to the object-glass of the camera, the Admiral
made him look at an object 45° ! to the right, and took a
second picture. When these pictures were placed in the
stereoscope, and viewed " without ceasing, turning first to
the right and then to the left, the eyes of the portrait
follow this motion as if they were animated." * This fact
must have been noticed in common stereoscopic portraits
by every person who has viewed them alternately with each
eye, but it is not merely the eyes which move. The nose,
and indeed every feature, changes its place, or, to speak
more correctly, the whole figure leaps from the one binocu-
lar position into the other. As it is unpleasant to open
and shut the eyes alternately, the same effect may be more
agreeably produced in ordinary portraits by merely inter-
cepting the light which falls upon each picture, or by
making an opaque screen pass quickly between the eyes
and the lens, or immediately below the lens, so as to give
successive vision of the pictures with each eye, and with
' Cosmos, Feb. 29, 1856, vol. viii. p. 202.
CHAP. VIII. RULES FOR BINOCULAR PICTURES. 155
both. The motion of the light reflected from the round
eyeball has often a striking effect.
From these discussions, our readers will observe that the
science, as well as the art of binocular portraiture for the
stereoscope, is in a transition state in which it cannot long
remain. The photographer who works with a very large
lens chooses an angle which gives the least unfavourable
results ; his rival, with a lens of less size, chooses, on the
same principle, a different angle ; and the public, who are
no judges of the result, are delighted with their pictures in
relief, and when their noses are either pulled from their
face, or flattened upon their cheek, or when an arm or a
limb threatens to escape from their articulation, they are
assured that nature and not art is to blame.
We come now to consider under what circumstances the
photographer may place the lenses of his binocular camera
at a greater distance than 2\ inches, or his two cameras
at a greater angle than that which we have fixed.
1. In taking family portraits for the stereoscope, the
cameras must be placed at an angle of 2° for 6 feet, when
the binocular camera is not used.
2. In taking binocular pictures of any object whatever,
when we wish to see them exactly as we do with our two
eyes, we must adopt the same method.
3. If a portrait is wanted to assist a sculptor in model-
ling a statue, a great angle might be adopted, in order to
shew more of the head. But in this case the best way
would be to take the correct social likeness, and then take
photographs of the head in different azimuths.
If we wish to have a greater degree of relief than we
have with our two eyes, either in viewing colossal statues,
156 RULES FOR BINOCULAR PICTURES. CHAP. VIII.
or buildings, or landscapes, where the deviation from nature
does not, as in the human face, affect the expression, or
injure the effect, we must increase the distance of the lenses
in the binocular camera, or the angle of direction of the
common camera. Let us take the case of a colossal statue
10 feet wide, and suppose that dissimilar drawings of it
about three inches wide are required for the stereoscope.
These drawings are forty times narrower than the statue,
and must be taken at such a distance, that with the bino-
cular camera the relief would be almost evanescent. We
must therefore suppose the statue to be reduced n times,
and place the semi-lenses at the distance n x 2\ inches. If
n = 10, the statue 10 feet wide will be reduced to \% or
to 1 foot, and n X 2£, or the distance of the semi-lenses
will be 25 inches. With the lenses at this distance, the
dissimilar pictures of the statue will reproduce, when com-
bined, a statue one foot wide, which will have exactly the
same appearance and relief as if we had viewed the colossal
statue with eyes 25 inches distant. But the reproduced
statue will have also the same appearance and relief as a
statue a foot wide reduced from the colossal one with
mathematical precision, and it will therefore be a better or
more relieved representation of the work of art than if we
had viewed the colossal original with our own eyes, either
under a greater, an equal, or a less angle of apparent
magnitude.
We have supposed that a statue a foot broad will be
seen in proper relief by binocular vision ; but it remains to
be decided whether or not it would be more advantageously
seen if reduced with mathematical precision to a breadth of
2% inches, the width of the eyes, which gives the vision of
CHAP. Vm. SINGLE-LENS BINOCTTLAB CAMERA. 157
a hemisphere ty inches in diameter with the most perfect
relief. 1 If we adopt this principle, and call b the breadth of
the statue of which we require dissimilar pictures, we must
make n = ^, and n X 2J = b, that is, the distance of the
semi-lenses in the binocular camera, or of the lenses in two
cameras, must be made equal to the breadth of the statue.
In concluding this chapter, it may be proper to remark,
that unless we require an increased relief for some special
purpose, landscapes and buildings should be taken with the
normal binocular camera, that is, with its lenses 2\ inches
distant. Scenery of every kind, whether of the picturesque,
or of the sublime, cannot be made more beautiful or grand
than it is when seen by the traveller himself. To add an
artificial relief is but a trick which may startle the vulgar,
but cannot gratify the lover of what is true in nature and
in art.
The Single Lens Binocular Camera.
As every photographer possesses a camera with a lens
between 2\ and 3 inches in diameter, it may be useful to
him to know how he may convert it into a binocular in-
strument.
In a cover for the lens take two points equidistant from
each other, and make two apertures, c, d, Fig. 43, ^ths of
an inch in diameter, or of any larger size that may be
thought proper, though -& is the proper size. Place the
cover on the end of the tube, and bring the line joining the
apertures into a horizontal position. Closing one aperture,
take the picture of the sitter, or of the statue, through the
i It is only in a horizontal direction that we can see 180° of the hemisphere.
We would require a circle of eyes 2\ inches distant to see a complete hemisphere.
158 THE CAMERA MADE THE STEREOSCOPE. CHAP. Vm.
other, and when the picture is shifted aside by the usual
contrivances for this purpose, take the picture through the
other aperture. These will be good binocular portraits,
fitted for any stereoscope, but particularly for the Achromatic
Reading Glass Stereoscope. If greater relief is wanted, it
may be obtained in larger lenses by placing the two aper-
tures at the greatest distance which the diameter of the lens
will permit.
The Binocular Camera made the Stereoscope.
If the lenses of the binocular camera, when they are
whole lenses, be made to separate a little, so that the dis-
tance between the centres of their inner halves may be
equal to 2£ inches, they become a lenticular stereoscope, in
which we may view the pictures which they themselves
create. The binocular pictures are placed in the camera
in the very place where their negatives were formed, and
the observer, looking through the halves of his camera
lenses, will see the pictures united and in relief. If the
binocular camera is made of semi-lenses, we have only to
place them with their thin edges facing each other to ob-
tain the same result. It will appear, from the discussions
in the following chapter, that such a stereoscope, indepen-
dently of its being achromatic, if the camera is achromatic,
will be the most perfect of stereoscopic instruments.
The preceding methods are equally applicable to land-
scapes, machines, and instruments, and to solid constructions
of every kind, whether they be the production of nature or
of Art. 1
1 See Chapters X. and XI.
CHAP. tX. ADAPTATION OF PICTURES TO STEREOSCOPE. 159
CHAPTER IX.
ON THE ADAPTATION OP THE PICTURES TO THE STEREOSCOPE.
THEIR SIZE, POSITION, AND ILLUMINATION.
Having described the various forms of the stereoscope,
and the method of taking the binocular portraits and pic-
tures to which it is to be applied, we have now to consider
the relation that ought to exist between the instrument and
the pictures, — a subject which has not been noticed by pre-
ceding writers.
If we unite two dissimilar pictures by the simple con-
vergency of the optical axes, we shall observe a certain
degree of relief, at a certain distance of the eyes from the
pictures. If we diminish the distance, the relief diminishes,
and if we increase it, it increases. In like manner, if we
view the dissimilar pictures in the lenticular stereoscope,
they have a certain degree of relief ; but if we use lenses of
a higher magnifying power, so as to bring the eyes nearer
the pictures, the relief will diminish, and if we use lenses
of a less magnifying power, the relief will increase. By
bringing the eyes nearer the pictures, which we do by mag-
nifying them as well as by approaching them, we increase
the distance between similar points of the two pictures, and
therefore the distance of these points, when united, from
160 EFFECT OF MAGNIFYING THE PICTtJKES. CHAP. IX.
any plane in the picture, that is, its relief will be dimi-
nished. For the same reason, the diminution of the dis-
tance between similar points by the removal of the eyes
from the picture, will produce an increase of relief. This
will be readily understood if we suppose the eyes R, l, in
Fig. 24, to be brought nearer the plane mn, to r' l', the
points 1, 1 and 2, 2 will be united at points nearer mn
than when the eyes were at e, l, and consequently their
relief diminished.
Now we have seen, that in taking portraits, as explained
in Fig. 45, we view the two pictures, a 6, a' b', with the
eyes at e and E', exactly, and with the same relief in the
air, as when we saw the original a b, from l, l', and there-
fore ec is the distance at which the dissimilar pictures
should be viewed in the stereoscope, in order that we may
see the different parts of the solid figure under their proper
relief. But the distance ec = lc is the conjugate focal
length of the lens l, if one lens is used, or the conjugate
equivalent focal length, if two achromatic lenses are used ;
and consequently every picture taken for the stereoscope
should be taken by a camera, the conjugate focal length of
whose lens corresponding to the distance of the sitter, is
equal to Jive inches, when it is to be used in the common
stereoscope, which has generally that depth.
Between the pictures and the purely optical part of the
stereoscope, there are other relations of very considerable
importance. The exclusion of all external objects or sources
of light, excepting that which illuminates the pictures, is a
point of essential importance, though its advantages have
never been appreciated. The spectacle stereoscope held in
the hand, the reflecting stereoscope, and the open lenticular
CHAP. IX. ILLUMINATION OP THE PICTUKES. 161
stereoscope, are all, in this respect, defective. The bin-
ocular pictures must be placed in a dark box, in order to
produce their full effect ; and it would be a great improve-
ment on the lenticular stereoscope, if, on the left and right
side of each eye-tube, a piece of brass were to be placed, so
as to prevent any light from entering the left angle of the
left eye, and the right angle of the right eye. 1 The eyes,
thus protected from the action of all external light, and
seeing nothing but the picture, will see it with a distinctness
and brilliancy which could not otherwise be obtained.
The proper iUuminatftn of the picture, when seen by re-
flected light, is also a point of essential importance. The
method universally adopted in the lenticular stereoscope is
not good, and is not the one which I found to be the best,
and which I employed in the first-constructed instruments.
The light which falls upon the picture is prevented from
reaching the observer only by its being incident at an angle
greater or less than the angle of reflexion which would
carry it to his eyes. A portion of the scattered light, how-
ever, does reach the eye, and in Daguerreotypes especially,
when any part of the surface is injured, the injury, or any
other imperfection in the plate, is more distinctly seen.
The illumination should be lateral, either by a different
form of window in the front, or by openings on the two
sides, or by both these methods.
When the lenticular stereoscope is thus fitted up, and
the pictures in this manner illuminated, the difference of
effect is equally great as it is between a picture as commonly
» When any external light falls upon the eye, its picture is reflected back from
the metallic surface of the Daguerreotype, and a negative picture of the part
of (he Daguerreotype opposite each eye is mixed with the positive picture of the
same part.
L
162 ON THE SIZE OP THE PICTUBES. CHAP. IX.
seen, and the same picture exhibited as a panorama or a
diorama, in which no light reaches the eyes but that which
radiates from the painting itself, the reflexion from the
varnish being removed by oblique or lateral illumination.
The great value of transparent binocular slides, when the
picture is to be upon glass, is obvious from the preceding
considerations. The illumination is uniform and excel-
lent, but care must be taken to have the ground glass in
front of the picture, or the paper, when it is used, of a very
fine grain, so that it may throw no black specks upon the
sky or the lights of the picture. Another advantage of the
transparent slides is, that the pictures are better protected
from injury than those upon paper.
It is obvious from these considerations that the me of
the pictures is determined, as well as the distance at which
they are to be viewed. Much ignorance prevails upon this
subject, both among practical photographers and optical
writers. Large binocular pictures have been spoken of as
desirable productions, and it has been asserted, and claimed
too, as a valuable property of the reflecting stereoscope,
that it allows us to use larger pictures than other instru-
ments. There never was a greater mistake. If we take a
large picture for the stereoscope we must place it at a great
distance from the eye, and consequently use a large stereo-
scope. A small picture, seen distinctly near the eye, is the
very same thing as a large picture seen at a greater distance.
The size of a picture, speaking optically and correctly, is
measured by the angle which it subtends at the eye, that
is its apparent magnitude. A portrait three inches high,
for example, and placed in the lenticular stereoscope five
inches from the eye, has the same apparent size as a Kit
CHAP. DL SIZE OF THE BINOCULAB PICTURES. 163
Cat portrait in oil the size of life, three feet high, seen at
the distance of five feet, the distance at which it is com-
monly examined ; and if we increase the magnifying power
so as to see the three-inch picture at the distance of two
inches, it will have the same apparent size as the three feet
oil portrait seen at the distance of two feet. If the pictures
used in the stereoscope were imperfect pictures that would
not bear being magnified, it would be improper to use
them ; but the Daguerreotypes, and the transparent pictures,
which are taken by the first artists, for the lenticular stereo-
scope, will bear a magnifying power ten times greater than
that which is applied to them.
If we take a large picture for the stereoscope, we are
compelled by pictorial truth to place it at a distance from
the eye equal to the equivalent focal distance of the camera.
Every picture in every camera has the same apparent mag-
nitude as the object which it represents ; whether it be a
human figure, or the most distant landscape ; and if we de-
sire to see it in its true relief in the stereoscope, we must
place it at a distance from the eye equal to the focal length of
the lens, whether it be an inch or a foot high. There is,
therefore, nothing gained by using large pictures. There
is, on the contrary, much inconvenience in their use. They
are in themselves less portable, and require a larger stereo-
scope; and we believe, no person whatever, who is ac-
quainted with the perfection and beauty of the binocular
slides in universal use, would either incur the expense, or
take the trouble of using pictures of a larger size.
In the beautiful combination of lenticular stereoscopes,
which was exhibited by Mr. Claudet, Mr. Williams, and
others, in the Paris Exhibition, and into which six or eight
164 STEREOSCOPIC TRAVELLING. CHAP. IX,
persons were looking at the same time, binocular pictures
of a larger size could not have been conveniently used.
But, independently of these reasons, the question of large
pictures has been practically settled. No such pictures
are taken by the Daguerreotypists or Talbotypists, who are
now enriching art with the choicest views of the antiquities,
and modern buildings, and picturesque scenery of every
part of the world ; and even if they could be obtained, there
are no instruments fitted for their exhibition. In the
magnificent collection of stereoscopic pictures, amounting to
above a thousand, advertised by the London Stereoscopic
Company, there are no fewer than sixty taken in Rome, and
representing, better than a traveller could see them there,
the ancient and modern buildings of that renowned city.
Were these sixty views placed on the sides of a revolving
polygon, with a stereoscope before each of its faces, a score
of persons might, in the course of an hour, see more of
Rome, and see it better, than if they had visited it in per-
son. At all events, those who are neither able nor willing
to bear the expense, and undergo the toil of personal travel,
would, in such a panorama, — an analytical view of Rome,
— acquire as perfect a knowledge of its localities, ancient
and modern, as the ordinary traveller. In the same man-
ner, we might study the other metropolitan cities of the
world, and travel from them to its river and mountain
scenery, — admiring its noble castles in our descent of the
Rhine, — its grand and wild scenery on the banks of the
Mississippi, or the Orinoco, — the mountain gorges, the
glaciers, and the peaks of the Alps and the Ural, — and the
more sublime grandeur which reigns among the solitudes of
the Himalaya and the Andes.
CHAP. IX. GENERAL STEREOSCOPIC LAW. 165
The following general rule for taking and combining
binocular pictures is the demonstrable result of the principles
explained in this chapter : —
Supposing that the camera obscura employed to take
binocular portraits, landscapes, dec, gives perfect representa-
tions of them, the relief picture in the stereoscope, produced
by their superposition and binocular union, will not be
correct and truthful, unless the dissimilar pictures are
placed in the stereoscope at a distance from the eyes, equal
to the focal distance, real or equivalent, of the object-glass
or object-glasses of the camera, and, whatever be the size of
the pictures, they will appear, when they are so placed, of
the same apparent magnitude, and in the same relief, as
when they were seen from the object-glass of the camera by
the photographer himself.
166 APPLICATION OP STEEEOSCOPE TO PAINTING. CHAP. X.
CHAPTER X.
APPLICATION OF THE STEREOSCOPE TO PAINTING.
Having explained the only true method of taking bin-
ocular portraits which will appear in correct relief when
placed in the stereoscope, we shall proceed in this chapter
to point out the application of the stereoscope to the art of
painting in all its branches. In doing this we must not
forget how much the stereoscope owes to photography, and
how much the arts of design might reasonably expect from
the solar pencil, when rightly guided, even if the stereoscope
had never been invented.
When the processes of the Daguerreotype and Talbotype,
the sister arts of Photography, were first given to the world,
it was the expectation of some, and the dread of others,
that the excellence and correctness of their delineations would
cast into the shade the less truthful representations of the
portrait and the landscape painter. An invention which
supersedes animal power, or even the professional labour of
man, might have been justly hailed as a social blessing, but
an art which should supersede the efforts of genius, and
interfere with the exercise of those creative powers which
represent to us what is beautiful and sublime in nature,
would, if such a thing were possible, be a social evil.
The arts of painting, sculpture, and architecture have in
CHAP. X. APPLICATION OF STEREOSCOPE TO PAINTING. 167
every age, and in every region of civilisation, called into
exercise the loftiest genius and the deepest reason of man.
Consecrated by piety, and hallowed by affection, the choicest
productions of the pencil and the chisel have been preserved
by the liberality of individuals and the munificence of
princes, while the palaces of sovereigns, the edifices of social
Hfe, the temples of religion, the watch-towers of war, the
obelisks of fame, and the mausolea of domestic grief, stand
under the azure cupola of heaven, to attest by their living
beauty, or their ruined grandeur, the genius and liberality
which gave them birth. To the cultivation and patronage
of such noble arts, the vanity, the hopes, and the holiest
affections of man stand irrevocably pledged ; and we should
deplore any invention or discovery, or any tide in the
nation's taste, which should paralyse the artist's pencil, or
break the sculptor's chisel, or divert into new channels the
genius which wields them. But instead of superseding the
arts of design, photography will but supply them with new
materials, — with collections of costume, — with studies of
drapery and of forms, and with scenes in life, and facts in
nature, which, if they possess at all, they possess imper-
fectly, and without which art must be stationary, if she
does not languish and decline.
Sentiments analogous to these have been more profes-
sionally expressed by M. Delaroche, a distinguished French
artist, — by Sir Charles Eastlake, whose taste and knowledge
of art is unrivalled, — and by Mr. Ruskin, who has already
given laws to art, and whose genius is destined to elevate
and to reform it. M. Delaroche considers photography
"as carrying to such perfection certain of the essential
principles of art, that they must become subjects of study
168 APPLICATION OP STEREOSCOPE TO PAINTING. CHAP. X.
and observation, even to the most accomplished artist."
. . . . " The finish of inconceivable minuteness," he says,
" disturbs in no respect the repose of the masses, nor im-
pairs in any way the general effect. .... The correctness
of the lines, the precision of the forms in the designs of
M. Daguerre, are as perfect as it is possible they can be,
and yet, at the same time, we discover in them a broad and
energetic manner, and a whole equally rich in hue and in
effect. The painter will obtain by this process a quick
method of making collections of studies, which he could not
otherwise procure without much time and labour, and in a
style very far inferior, whatever might be his talents in
other respects." In the same spirit, Mr. Buskin 1 considers
" the art of photography as enabling us to obtain as many
memoranda of the facts of nature as we need ;" and long
before Mr. Talbot taught us to fix upon paper the pictures
of the camera obscura, the Rev. John Thomson, one of the
most distinguished of our Scottish landscape painters,
studied, in one of these instruments, the forms and colours
of the scenes which he was to represent. Other artists,
both in portrait and in landscape, now avail themselves of
photography, both as an auxiliary and a guide in their pro-
fession ; but there are certain difficulties and imperfections
in the art itself, and so many precautions required in its
right application, whether we use its pictures single, as re-
presentations on a plane, or take them binocularly, to be
raised into relief by the stereoscope, that we must draw from
the principles of optics the only rules which can be of real
services to the arts of design.
In painting a landscape, a building, a figure, or a group
1 Modern Painters, vol. ill, Pre&ce, pp. 11, 12.
CHAP. X. APPLICATION OP STEREOSCOPE TO PAINTING. 169
of figures, the object of the artist is to represent it on his
canvas just as he sees it, having previously selected the best
point of view, and marked for omission or improvement
what is* not beautiful, or what would interfere with the
effect of his picture as a work of high art. His first step,
therefore, is to fix upon the size of his canvas, or the dis-
tance at which the picture is to be seen, which determines
its size. His own eye is a camera obscura, and the rela-
tion between the picture or image on its retina is such,
that if we could view* it from the centre of curvature of the
retina, (the centre of visible direction,) a distance of half an
inch, it would have precisely the same apparent magnitude
as the object of which it is the image. Let us now sup-
pose that the artist wishes to avail himself of the picture
in the camera obscura as received either on paper or ground
glass, or of a photograph of the scene he is to paint. He
must make use of a camera whose focal length is equal to
the distance at which his picture is to be seen, and when
the picture thus taken is viewed at this distance (suppose
two feet) it will, as a whole, and in all its parts, have the
same apparent magnitude as the original object This will
be understood from Fig. 47, in which we may suppose h
to be the lens of the camera, bb the object, and ny 1 the
distance at which it is to be viewed. The size of the
picture taken with a lens at h, whose focal length is h^,
will be 6V, and an eye placed at h will see the picture 6V
under an angle b's.i\ equal to the angle bhb, under which
the real object bb was seen by the artist from h. In like
manner, a larger picture, byr, taken by a camera the focal
distance of whose lens at H is Hy, will be an accurate
representation of the object bb, when viewed from h, and of
170 APPLICATION OP STEREOSCOPE TO PAJNTOTG. CHAP. X.
the same apparent magnitude. If either of these pictures,
b V or b r, are viewed from greater or less distances than
Hy, or Hy, they will not be correct representations of the
Fio. 47.
object rb, either in apparent magnitude or form. That
they will be of a different apparent magnitude, greater
when viewed at less distances than Hy*, h$t, and less when
viewed at greater distances, is too obvious to require any
illustration. That they will differ in form, or in the relative
apparent size of their parts, has, so far as I know, not
been conjectured. In order to shew this, let us suppose a
man six feet high to occupy the foreground, and another
of the same size to be placed in the middle distance, the
distance of the two from the artist being ten and twenty
feet. The apparent magnitudes of these two men on the
photograph will be as two to one ; and if we look at it at
any distance greater or less than the focal length YLjf of the
lens, the same proportion of two to one will be preserved,
whereas if we look at the original figures at a greater or
less distance from them than the place of the artist, the
CHAP. X. APPLICATION OF STEREOSCOPE TO PAINTING. 171
ratio of their apparent magnitudes will be altered. If the
artist, for example, advances five feet, the nearest man will
be five feet distant and the other fifteen feet, so that their
apparent magnitude will now be as three to one.
The same observations apply to a portrait of the human
face. In looking at a human profile let us suppose the
breadth of the nose to be one inch, that of the ear one
inch, and that we view this profile at the distance of three
feet from the ear, which is two inches nearer the observer
than the nose. The apparent magnitude of the ear and
nose will be as thirty-eight to thirty-six inches, whereas
if we view the profile from the distance of one foot the
ratio will be as fourteen to twelve, that is, the ear will be
increased in apparent size more than the nose. Hence it
follows that all pictures should be viewed under the same
angle of apparent magnitude under which they were seen
by the artist as taken photographically, for if we view
them at a greater or less angle than this we do not see the
same picture as when we looked at the original landscape
or portrait, under the same angle of apparent magnitude.
From the observations made in the preceding Chapter
on photographic and stereoscopic portraiture, the reader
must have already drawn the inference that the same
landscape or building, seen at different distances, varies
essentially in its character, — beauties disclosing themselves
and defects disappearing as we approach or recede from
them. The picture in the camera, therefore, as used by
Mr. Thomson, or, what is still better, with the exception of
colour, the photograph obtained by the same instrument,
will supply the artist with all the general materials for his
picture. The photograph will differ considerably from any
172 APPLICATION OP STEREOSCOPE TO PAINTING. CHAP. X.
sketch which the artist may have himself made, owing to
certain optical illusions to which his eye is subject. The
hills and other vertical lines in the distance will be lower
in the photograph than in his sketch. 1 The vertical lines
of buildings will converge upwards in the photograph, as
they ought to do, in receding from the eye ; and in the
same picture there will be a confusion, as we shall after-
wards shew, in the delineation of near and minute objects
in the foreground, increasing with the size of the lens which
he has employed.
In his admirable chapter " On Finish," Mr. Ruskin has
established, beyond a doubt, the most important principle
in the art of painting. " The finishing of nature," he
states, " consists not in the smoothing of surface, but the
filling of space, and the multiplication of life and thought ;"
and hence he draws the conclusion, that " finishing means,
in art, simply telling more truth." Titian, Tintoret, Bellini,
and Veronese have, as he has shewn, wrought upon this
principle, delineating vein by vein in the leaf of the vine,
petal by petal in the borage-blossoms, the very snail-shells
on the ground, the stripe of black bark in the birch-tree,
and the clusters of the ivy-leaved toad-flax in the rents of
their walls ; and we have seen that a modern artist, Dela-
roche, considers a finish of inconceivable minuteness as
* Sir Francis Chantrey, the celebrated sculptor, shewed me, many years ago, a
Sketch-Book, containing numerous drawings which he had made with the Camera
Lucida, while travelling from London to Edinburgh by the Lakes. He pointed
out to me the flatness, or rather lowness, of hills, which to his own eye appeared
much higher, but which, notwithstanding, gave to him the idea of a greater eleva-
tion. In order to put this opinion to the test of experiment, I had drawings
made by a skilful artist of the three Eildon hills opposite my residence on
tbe Tweed, and wassurprised to obtain, by comparing them with their true perspec-
tive outlines, a striking confirmation of the observation made by Sir Francis
Chantrey.
CHAP. X. APPLICATION OF STEREOSCOPE TO PAINTING. 173
neither disturbing the repose of the masses, nor interfering
with the general effect in a picture.
The Pre-Raphaelites, therefore, may appeal to high
authority for the cardinal doctrine of their creed ; and what-
ever be their errors in judgment or in taste, they have
inaugurated a revolution which will release art from its
fetters, and give it a freer and a nobler aim. Nature is too
grand in her minuteness, and too beautiful in her humility,
to be overlooked in the poetry of art. If her tenderest and
most delicate forms are worthy of admiration, she will de-
mand from the artist his highest powers of design. If the
living organizations of the teeming earth, upon which we
hourly tread, are matchless in structure, and fascinating in
colour, the palette of the painter must surrender to them
its choicest tints. In the foreground of the highest art,
the snail-shell may inoffensively creep from beneath the
withered leaf or the living blade; the harebell and the
violet may claim a place in the sylvan dell ; the moss may
display its tiny frond, the gnarled oak or the twisted pine
may demand the recognition of the botanist, while the castle
wall rises in grandeur behind them, and the gigantic cliffs
or the lofty mountain range terminate the scene.
If these views are sound, the man of taste will no longer
endure slovenliness in art. He will demand truth as well
as beauty in the landscape ; and that painter may change
his profession who cannot impress geology upon his rocks,
and botany upon his plants and trees, or who refuses to
display, upon his summer or his autumn tablet, the green
crop as well as the growing and the gathered harvest. Thus
enlarged in its powers and elevated in its purposes, the art
of painting will be invested with a new character, demand-
174 APPLICATION OP STEREOSCOPE TO PAINTING. CHAP. X.
ing from its votaries higher skill and more extended know-
ledge. In former times, the minute and accurate delinea-
tion of nature was a task almost impossible, requiring an
amount of toil which could hardly be repaid even when
slightly performed ; but science has now furnished art with
the most perfect means of arresting, in their most delicate
forms, every object, however minute, that can enter into the
composition of a picture. These means are the arts of
photography and stereoscopic re-combination, when rightly
directed, and it is the object of the present chapter to shew
how the artist may best avail himself of their valuable and
indispensable aid.
Every country and district, and even different parts of the
same district, have a Flora and Geology peculiar to them-
selves; and the artist who undertakes to represent its beau-
ties owes to truth the same obligations as the botanist who
is to describe its plants, or the mineralogist its rocks and
stones. The critic could not, in former times, expect more
details from his unaided pencil than it has generally fur-
nished ; but with the means now at his command, he must
collect, like the naturalist, all the materials for his subject.
After the camera has given him the great features of his
landscape, he must appeal to it for accurate delineations of
its minuter parts, — the trunks, and stems, and leafage of
his trees — the dipping strata of its sandstone beds — the
contortions of its kneaded gneiss, or the ruder features of
its trap and its granite. For the most important of these
details he will find the camera, as at present constructed,
of little service. It is fitted only to copy surfaces ; and
therefore, when directed to solid bodies, such as living
beings, statues, &c, it gives false and hideous representa-
CHAP. X. APPLICATION OF STEREOSCOPE TO PAINTING. 175
tions of them, as I hare shewn in a preceding chapter. It
is peculiarly defective when applied to parts of bodies at
different distances from it, and of a less diameter than the
lens. The photograph of a cube taken by a lens of a greater
diameter, will display Jfoe of its sides in a position, when its
true perspective representation is simply a single square of
its surface. When applied to trees, and shrubs, and flowers,
its pictures are still more unsatisfactory. Every stem and
leaf smaller than the lens, though absolutely opaque, is
transparent, and leaves and stems behind and beyond are
seen like ghosts through the photographic image.
This will be understood from Fig. 48, in which ll is the
Fig. 48.
lens of the camera, ab the breadth of the trunk or stem of
a tree less than ll in width. Draw la, lb, touching ab
in the points A, b, and crossing at c. Objects behind ab,
176 APPLICATION OP STEREOSCOPE TO PAINTING. CHAP. X.
and placed within the angle acb, will not have any images
of them formed by the lens ll, because none of the rays
which proceed from them can mil upon the lens, but objects
placed within the angle ecf, however remote be their dis-
tance, will have images of them formed by the lens. If d,
for example, be a leaf or a fruit, or a portion of a branch,
the rays which it emits will fall upon the portions Lm, in
of the lens, determined by drawing Dm, j>n touching ab,
and an image of it will be formed in the centre of the photo-
graphic image of ab, as if ab were transparent This image
will be formed by all the portions of the surface of the lens
on which the shadow of ab, formed by rays emanating from
d, would not fall If the object d is more remote, the shadow
of ab will diminish in size, and the image of the object will
be formed by a greater portion of the lens. If the sun were
to be in the direction m n, his image would appear in the
centre of the trunk or stem, corresponding to ab, Fig. 49.
If the stem occupies any other position, ab, Fig. 48, in the
landscape, objects, such as d, within the angle ecf, will have
CHAP. X. APPLICATION OF STEREOSCOPE TO PAINTING. 177
images of them formed within the corresponding portion of
the trunk or stem. Hence, if ab, Fig. 49, represents the
shadow of the stem across the lens ll, the image of any
object, which if luminous would give this shadow, will be
formed within the photographic image of the stem, and as
every part of it may have branches, or leaves, or fruit behind
it, its photographs will be filled with their pictures, which
will have the same distinctness as other equidistant parts
of the landscape.
These observations are applicable to the limbs and slender
parts of animate and inanimate figures, when they are of a
less size than the lens with which their photograph is taken.
They will be transparent to all objects behind them, and
their true forms and shades cannot be taken with the
cameras now in use. 1
In order, therefore, to collect from nature the materials
of his profession, the artist must use a camera with a lens
not much larger than the pupil of his eye, and with such
an instrument he will obtain the most correct drawings of
the trunks and stems of trees, of the texture and markings
of their bark, of the form of their leaves, and of all those
peculiarities of structure and of leafage by which alone the
trees of the forest can be distinguished. In like maimer,
he will obtain the most correct representations of the rocks
and precipices, and the individual stones 2 which may enter
i By using large lenses, we may obtain the picture of an object within the picture
of an opaque one in front of it ; and with a telescope, we may Bee through opaque
objects of a certain size. Many singular experiments may be made by taking pho-
tographs of solid objects, simple or compound, with lenses larger than the objects
themselves.
3 In a landscape by Mr. Waller Paton, called the " Highland Stream," now in
the Edinburgh Exhibition, the foreground consists principally of a bed of water-
worn stones, on the margin of a pool at the bottom of a waterfall. The stones are
M
178 APPLICATION OF STEREOSCOPE TO PAINTING. CHAP. X.
into his picture, — of the plants which spring from their
crevices or grow at their base, and of those flowers in their
native grace and beauty, which hitherto he has either drawn
from recollection, or copied from the formal representations
of the botanist.
In addition to their correctness as true representations of
natural forms, photographs have a peculiar value, for which
no labour or skill on the part of the artist can compensate.
In drawing the sketch of a landscape, or delineating the
trees, rocks, and foliage which are near him, or the objects
in the middle or remote distance, several hours must be
spent. During this period, the landscape and its individual
parts are undergoing no inconsiderable change. A breeze may
disturb the masses of his foliage, and bend his tree stems,
and ruffle his verdure, and throw new reflected lights upon
the waving crops, while every direct light is changing in in-
tensity and direction during the culmination or descent of
the sun. What he has delineated in the morning will
hardly correspond with what he draws at noon, and the
distances which at one time are finely marked in aerial
perspective, will disappear, or even suffer inversion by
variations in the intensity and position of the haze. If
cottages, or castles, or buildings of any kind, enter into the
picture, the shadows of their projections, and the lights upon
their walls and roofs will, in sunshine, undergo still greater .
variations, and the artist will be perplexed with the ana-
chronisms and inconsistencies of his choicest materials. The
so exquisitely painted, that nature only could have furnished the originals. We
may examine them at a few inches' distance, and recognise forms and structures
with which we have been long familiar. A water-ousel, peculiar to Scottish brooks
and rivers, perched upon one of them, looks as anxiously around as if a schoolboy
were about to avail himself of the missiles at his feet.
CHAP. X. APPLICATION OF STEREOSCOPE TO PAINTING. 179
landscape thus composed in patches will, in its photograph,
have a very different aspect, as much in its forms as in its
lights and shadows. The truths of nature are fixed at one
instant of time ; the self-delineated landscape is embalmed
amid the co-existing events of the physical and social world.
If the sun shines, his rays throw their gilding on the pic-
ture. If the rain-shower falls, the earth and the trees
glisten with its reflexions. If the wind blows, the partially
obliterated foliage will display the extent of its agitation.
The objects of still life, too, give reality and animation to
the scene. The streets display their stationary chariots,
the esplanade its military array, and the market-place its
colloquial groups, while the fields are studded with the
forms and attitudes of animal life. The incidents of time
and the forms of space are thus simultaneously recorded,
and every picture from the sober palette of the sun becomes
an authentic chapter in the history of the world. 1
But, however valuable photography has become to the
artist, science has recently given him another important
auxiliary. In order to make this available, he must em-
ploy a small pocket binocular camera, to take double
pictures to be united in the stereoscope. His trees will
thus exhibit the roundness of their trunks and stems, the
leaves and branches will place themselves at their proper
distance, and he will discover the reason of peculiar effects
which in the plane photograph he has been unable to
understand. Seeing that his own picture is to be upon a
plane surface, I can hardly expect to convince the artist
that he will obtain more information by reproducing the
i These views are well illustrated by the remarkable photographs of the Crimean
war.
180 APPLICATION OF STEREOSCOPE TO PAINTING. CHAP. X.
original in relief It is a fact, however, beyond dispute,
that effects are produced by the stereoscopic union of two
plane photographs which are invisible in the single picture.
These effects, which are chiefly those of lustre and shade,
are peculiarly remarkable in Daguerreotype, and it is by no
means easy to explain the cause. In a Daguerreotype, for
example, of two figures in black bronze, with a high metallic
lustre, it is impossible, by looking at the single picture, to
tell the material of which they are made ; but the moment
they are united into stereoscopic relief their true character
is instantly seen. In a Daguerreotype of Alexander and
Bucephalus, portions of the figure seem as if shaded with
China ink of a nearly uniform tint, but when seen in relief
the peculiar shade entirely disappears. The stereoscopic
combination of two surfaces of different intensities, though
of the same colour, produces effects which have not yet
been sufficiently studied. But, independently of these
peculiarities, the artist will certainly derive more aid from
his landscape in relief and from the study of its individual
parts, in their roundness and relative distances, than when
he examines them in their plane representations. The
shadows which the branches of leaves cast upon the trunks
and stems of his trees he will be able to trace to the
causes which produce them. Effects in outline, as well as
in light and shadow, which may perplex him, will find an
explanation in the relative distances and differences of
apparent magnitude of individual parts ; and, after becoming
familiar with his landscape in relief, as it exists in Nature,
he cannot mil to acquire new principles and methods of
manipulation. Nature flattened upon paper or metal, and
Nature round and plump, as if fresh from the chisel of the
CHAP. X. APPLICATION OF STEEBOSCOPB TO PAINTING. 181
Divine sculptor, must teach very different lessons to the
aspiring artist.
The historical painter, or the more humble artist who
delineates the scenes of common or domestic life, will
derive from the photographic camera and the stereoscope
advantages of equal importance. The hero, the sage, and
the martyr, drawn from living originals, may be placed in
the scenes where they suffered, or in the localities which
they hallowed. The lawgiver of Egypt, though he exists
only in the painter's eye, may take his place beside the
giant flanks of Horeb or the awe-inspiring summit of
Mount Sinai ; and He whom we may not name may chal-
lenge our love and admiration amid the sun-painted scenes
of his youth, of his miracles, and of his humiliation. The
fragments of ancient grandeur which time and war have
spared, the relics of bygone ages which have resisted the
destructive elements, will, as the materials of art, give
reality and truth to the pictorial history of times past,
while the painter of modern events can command the most
accurate representations not only of the costume, but of the
very persons of the great men whose deeds he is called
upon to immortalize. The heroes of the Crimean war,
whether friends or foes, will be descried in the trenches in
which they fought, amid the ranks which they led to vic-
tory, or among the wrecks of the fatal encounter in which
they fell. The sun will thus become the historiographer
of the future, and in the fidelity of his pencil and the
accuracy of his chronicle, truth itself will be embalmed and
history cease to be fabulous.
But even in the narrower, though not less hallowed
sphere of domestic life, where the magic names of kindred
182 APPLICATION OF STEBEOSCOPE TO PAINTING. CHAP. X.
and home are inscribed, the realities of stereoscopic photo-
graphy will excite the most thrilling interest. In the
transition forms of his offspring, which link infancy with
manhood, the parent will recognise the progress of his
mortal career, and in the successive phases which mark the
sunset of life, the stripling in his turn will read the lesson
that his pilgrimage too has a term which must close. Nor
are such delineations interesting only as works of art, or as
incentives to virtue; they are instinct with associations
vivid and endearing. The picture is connected with its
original by sensibilities peculiarly tender. It was the very
light which radiated from her brow, — the identical gleam
which lighted up her eye, — the hectic flush or the pallid
hue that hung upon her cheek, which pencilled the cherished
image, and fixed themselves for ever there.
CHAP. XI. APPLICATION OF STEREOSCOPE TO SCULPTURE. 1 83
CHAPTER XL
APPLICATION OF THE STEREOSCOPE TO SCULPTURE,
ARCHITECTURE, AND ENGINEERING.
To the arts of sculpture and architecture, the processes
of binocular photography and stereoscopic combination are
particularly applicable. The landscape painter has every day
within his reach examples of the picturesque, the wild and
the sublime in nature. In the fields which surround him,
in the river, or even in the " brook that bubbles by," on
the shore, on the heath, or on the mountain side, he has
the choice of materials for every department of his art.
The sculptor has no such advantage. Swathed in impene-
trable drapery the human figure mocks his eager eye, and it
is only by stolen glances, or during angel visits, few and
far between, that he can see those divine forms which it is
his business to portray. He must therefore quit his home
and seek for the models of ancient and modern art. In
the British Museum, in the Louvre, in the Vatican, and in
the repositories of art in Berlin, Munich, and other European
cities, he must spend months and years in the study of his
profession. He must copy, day after day, those master
triumphs of genius which the taste of ages has consecrated,
184 APPLICATION OP STEREOSCOPE TO SCULPTURE. CHAP. XI.
and gather from their study the true principles of his art.
Transferred to his own studio, these copies will be his
instructor and his guide. They will exhibit to him forms
more than human, though human still, embodying all that
is true and beautiful in what might be man. The value
of these copies, however, depends on the skill and care with
which they have been taken ; but no labour however great,
and no power of drawing however masterly, can give even
an approximate idea either of the outline or round of solid
figures, whether single or in groups. Light and shade can
alone evolve those muscular prominences, or those soft and
sphere-like relievos which give such power and beauty to
forms, male and female ; but how can an artist catch and
fix those lights and shades which give relief to the parts
which they illuminate or obscure ] The light of the sun,
even in a cloudless sky, is ever varying in intensity,
and the breadth and direction of the shadows which he
casts are varying from hour to hour. In a cloudy day, the
motion of the clouds, and the varying reflexions within his
apartment, subject the lights and shadows to constant
change. The portions of the drawing executed in the
morning will not harmonize with what is drawn at noon,
or during the decline of day. We consider it, therefore,
impossible to execute a drawing of a statue, or of a group
of statues, from which the artist can have anything like an
accurate idea of the forms which compose them.
From all these difliculties the sculptor has been relieved
by the invention of the photographic process. He may
thus take copies of statues in a few minutes, and take them
in all their aspects, and as seen at various distances, and
in this manner he will obtain drawings with the shadows as
CHAP. XL APPLICATION OF STEREOSCOPE TO SCULPTURE. 185
they existed at a particular instant, so that the lights and
shades, upon every individual part of the statue, will be
correctly related to each other. But valuable as these
drawings are, compared with those executed by the pencil,
their value becomes tenfold greater when they are taken
with the binocular camera, and with small lenses, as already
described. When combined in the stereoscope, he may re-
produce the statue in relief, in all its aspects, and of
different sizes, and derive from its study the same advan-
tages which the statue itself would have furnished. In
one respect the creations of the stereoscope surpass the
original. While the artist is surveying and drawing
instruction from the marble prototype, its lights and
shadows, and consequently the delicate forms, convex and
concave, by which they are produced, are constantly chang-
ing, whereas, in the stereoscopic statue, everything is fixed
and invariable. 1 In taking busts and statues from the
living subject, the sculptor will derive great advantage from
the stereoscope. Double pictures of the whole, or of any
portion of the subject, may be taken and raised into relief,
and from such binocular pictures, executed on one side of
the globe, an artist, on the other side, may complete an
admirable statue. The dying and the dead may thus be
modelled without the rude contact of a mask, and those
noble forms perpetuated which affection or gratitude has
endeared.
We must warn the sculptor, however, against the employ-
ment of binocular pictures taken with large lenses. Not
only will the individual picture be deformed, but a double
> A French sculptor has actually modelled a statue from the stereoscopic relief
of binocular pictures.
186 APPLICATION OF STEREOSCOPE TO SCULPTURE. CHAP. XI.
deformity will be induced by their union ; and whether he
copies from a statue or from a living figure, his work must
be defective, even to an ordinary eye.
In architecture, and all those arts in which ornamental
forms are given to solid materials, the binocular camera
and the stereoscope will be found indispensable. The
carvings of ancient, or mediaeval, or modern art may be
copied and reproduced in relief, whatever be the material
from which they have been cut. The rich forms of Gothic
architecture, and the more classical productions of Greek
and Roman genius, will swell the artist's portfolio, and
possess all the value of casts. With the aid of the Ka-
leidoscope the modern artist may surpass all his predeces-
sors. He may create an infinite variety of those forms of
symmetry which enter so largely into the decorative arts ;
and if the individual forms, which constitute the symmetrical
picture, are themselves solid, the binocular-kaleidoscopic
pictures, taken photographically, will be raised into the
original relief of their component parts, or they may be
represented directly to the eye in relief, by semi-lenses
placed at the ocular extremities of the reflecting plates. 1
If the symmetrical forms are taken from lines in the
same plane, no relief will be obtained from the kaleidoscopic
pictures.
But it is not merely to the decorative parts of architec-
ture that the stereoscope is applicable. The noblest edifices,
whether of a civil, a religious, or a military character, which
he could otherwise study only as a traveller, and repre-
sent in hurried and imperfect sketches, will, when taken
binocularly, stand before him in their full relief and gran-
1 See my Treatise on the Kaleidoscope, second edition, just published.
CHAP. XL APPLICATION OF STEREOSCOPE TO SCULPTURE. 1 87
deur, reflecting to his eye the very lights and shadows
which at a given hour the sun cast upon their walls.
In the erection of public buildings, hourly or daily pho-
tographs have been taken of them, to shew to the absent
superintendent the progress of his work ; but these pictures
will be still more expressive if binocular ones are combined
in the stereoscope.
To the engineer and the mechanist, and the makers of
instruments of all kinds, the stereoscope will be of ines-
timable value. The difficulty of representing machinery is
so great that it is not easy to understand its construction
or its mode of operation from plans and perspective views
of it. The union of one or two binocular pictures of it,
when thrown into relief, will, in many cases, remove the
difficulty both of drawing and understanding it. Photo-
graphs of machinery, however, consisting of a number of
minute parts at different distances from the eye, have, when
taken by large lenses, all the defects which we explained
in reference to trees and their branches and leaves. Sup-
ports and axles will be transparent, and the teeth of the
wheels, and the small and distant parts of the mechanism,
will be seen through all the nearer parts whose width is
less than the diameter of the lens.
In taking a binocular picture of a machine or instru-
ment consisting of various parts, that minute accuracy
which is necessary to give the true form and expression of
the human face is not required ; but if it should happen
that, in a correct binocular view of the object, parts are
concealed which it would be useful to see, we must dis-
cover the binocular angle which will shew these parts in
188 APPLICATION OP STEREOSCOPE TO 8CULPTURE. CHAP. XL
the two pictures, or, generally speaking, which will give
the best view of the mechanism, and then adjust the lenses
of the camera to give the desired representations of it.
These observations will be found useful in obtaining stereo-
scopic views of the structures in carpentry and ship-
building.
CHAP. XII. APPLICATION OF STEREOSCOPE TO NAT. HIST. 189
CHAPTER XII
APPLICATION OF THE STEREOSCOPE TO NATURAL
HISTORY.
In treating of those objects of natural history which
enter into the composition of landscape scenery, such as
trees, plants, and rocks, we have pointed out the method
of having them accurately drawn for the stereoscope ; but
it is to the importance of stereoscopic photography in
natural history as a science that we propose to devote the
present Chapter.
When we reflect upon the vast number of species which
have been described by zoologists, the noble forms of ani-
mated nature, whether wild or domesticated, and the
valuable services which many of them perform as the
slaves of man, we can hardly attach too much importance
to the advantage of having them accurately delineated
and raised into stereoscopic relief The animal painters of
the present day, — the Landseers, the Cowpers, and the
Ansdells, have brought this branch of their art to a high
degree of perfection, but the subjects of their pencil have
been principally dogs, horses, deer, and cattle, and a few
other animals, with which they are well acquainted, and
specimens of which were within their reach. To give
190 APPLICATION OP THE STEREOSCOPE CHAP. XII.
accurate representations of giraffes, hyaenas, and the rarer
animals which are found alive only in zoological gardens
and travelling caravans, is a more difficult task, and one
which has been necessarily intrusted to inferior hands. In
this branch of his art the photographer is perplexed with
the difficulty of arresting his subject in a position of repose
and in the attitude which he requires. But this difficulty
will diminish as his materials become more sensitive to
light ; and means may be found for fixing, without con-
straint, certain animals in the desired position. We have
seen the portrait of a dog taken with such minute accuracy
that the slightest trace of any motion could not be per-
ceived. Its master directed his attention to a piece of
bread, and he stood firmly waiting for his reward. Con-
sidering truth as an essential element in all photographs,
we are unwilling to counsel the artist to have recourse to
a large lens for the purpose of accelerating his process by
seizing his restless object in a single instant of time ; but
what cannot be tolerated in the human form may be per-
mitted in animal portraiture as a necessary evil. The
divine lineaments and delicate forms which in man the
intellect and the affections conspire to mould, are concealed
under the shaggy drapery of the world of instinct ; and
even if they existed and were perceived, could hardly be
appreciated by those who have not studied its manners and
submitted to its laws. But even in the present state of
photography such a celerity of process has been attained
that a distinguished amateur in Edinburgh has constructed
a portable camera, which, by pulling a trigger, instantane-
ously records upon its sensitive retina the surf which is
hurrying to the shore, or the stranger who is passing in the
CHAP. Xn. TO NATURAL HISTORY. 191
street. With such an instrument, in such hands, the
denizens of the jungle or of the plains may be taken
captive in their finest attitudes and in their most restless
moods. Photographs thus obtained will possess a value of
no ordinary kind, and when taken in the binocular camera
and raised into relief by the stereoscope, will be valuable
auxiliaries to the naturalist, and even to the painters and
the poets whose works or whose lyrics may require an
introduction to the brutes that perish.
In representing with accuracy the osteology and integu-
ments of the zoological world — the framework which pro-
tects life, and to which life gives activity and power, the
aid of the stereoscope is indispensable. The repose of death,
and the sharp pencil which resides in the small lens, will
place before the student's eye the skeleton, clothed or un-
clothed, in accurate perspective and true relief, while he
contemplates with wonder, in their true apparent magni-
tude, the gigantic Mastodon, the colossal Megatherion, and
the huge Dinornis, or examines the crushed remains of the
lengthened Saurian, or the hollow footsteps which ancient
life has impressed on the massive sandstone or the indurated
clay.
In the other branches of natural history, ichthyology,
ornithology, conchology, &c, the stereoscope will be found
equally useful. In entomology, where insects are to be
represented, the microscopic binocular camera must be used;
and in order to prevent the legs, the antennae, and other
small parts of the object from being transparent, and there-
fore spotted, with the images of objects or parts beyond
them, as explained in a preceding chapter, the smallest
lenses should be employed.
192 APPLICATION OF STEREOSCOPE TO NAT. HIST. CHAP. XII.
The roots and bulbs which are raised by the agriculturist
and the horticulturist, the turnip, the beet, the carrot, and
the onion ; and the fruits raised in the orchard, on the
wall, or in the hothouse, may be exhibited in all their
roundness and solidity in the stereoscope ; and as articles
of commerce they might be purchased on the authority of
their pictures in relief. The microscopic stereoscope will,
in like manner, give accurate magnified representations in
relief of grains and seeds of all kinds, and by comparing
these with the representations of those of a standard
form and quality, the purchaser may be enabled to form a
better idea of their excellence than if he saw them with
his own eyes, or had them in his own hands.
CHAP. Xm. USE OF THE STEREOSCOPE IN EDUCATION. 193
CHAPTEB XIII.
APPLICATION OP THE STEREOSCOPE TO EDUCATIONAL
PURPOSES.
The observations contained in the preceding chapters
prepare us for appreciating the value of the stereoscope as
an indispensable auxiliary in elementary as well as in pro-
fessional education. When the scholar has learned to read,
to write, and to count, he has obtained only the tools of
instruction. To acquire a general knowledge of the works
of God and of man — of things common and uncommon —
of the miracles of nature and of art, is the first step in the
education of the people. Without such knowledge, the
humblest of our race is unfit for any place in the social
scale. He may have learned to read his Bible, and he may
have read it after he had learned to read ; — he may have
committed to memory every sentence in the Decalogue ; —
he may have packed into the storehouse of his brain all the
wisdom of Solomon, and all the divine precepts of a greater
than Solomon, while he is utterly ignorant of everything
above him, around him, and within him, — ignorant, too, of
the form, the magnitude, and the motions of his terrestrial
home, — ignorant of the gigantic structures which constitute
the material universe, — ignorant of the fabrics which in-
dustry prepares for his use, and of the luxuries which com-
N
194 USE OF THE STEREOSCOPE IN EDUCATION. CHAP. XHL
merce brings from the ends of the earth and places at his
door, — ignorant even of the wonderful operations of that
beneficent commissariat, which is every moment, while he
sleeps and dreams, elaborating the materials by which he
is fed and clothed.
Were we to say, though we do not say it, that in our
own country the teachers, so penuriously endowed by the
State, are not much in advance of their pupils, we should
err only in stating what is not universally true ; and yet
there are men of influence and character insisting upon the
imposition of sectarian tests, and thus barricading our
schools against the admission of the wisest and the fittest
masters ! And while every civilized community in the
world is eagerly teaching their people, irrespective of reli-
gious creeds, the same bigots, civil and ecclesiastical, in our
own country, have combined to resist the only system of
education which can stem the tide of vice and crime which
is desolating the land.
Missionary labour and reformatory institutions, valuable
as they are, presuppose an educated community. To instruct
and reform a race that can neither read their Bible nor
derive knowledge from books, is a task beyond human
achievement The dearest interests of society, therefore,
call loudly for Secular Education, — the greatest boon which
philanthropy ever demanded from the State. The minister
who, in the face of sectarian factions, dares not identify him-
self with a large legislative measure for the education of the
people, and resigns office when he fails to carry it, prefers
power to duty, and, if he ever possessed it, divests himself
of the character of a statesman and a patriot He may be
justified in punishing the law-breaker who cannot read his
CHAP. Xm. USE OP THE STEREOSOOFE IN EDUCATION. 1 95
statutes, but he is himself the breaker of laws of a higher
order, and sanctioned by a higher tribunal
If the education of the people is to be attempted either
by partial or comprehensive legislation, the existing system
is utterly inefficient. The teacher, however wisely chosen
and well qualified, has not at his command the means of
imparting knowledge. He may pour it in by the ear, or
extract it from the printed page, or exhibit it in caricature in
the miserable embellishments of the school-book, but unless
he teaches through the eye, the great instrument of know-
ledge, by means of truthful pictures, or instruments, or
models, or by the direct exhibition of the products of nature
and of art, which can be submitted to the scrutiny of the
senses, no satisfactory instruction can be conveyed 1 Every
school, indeed, should have a museum, however limited and
humble. Even from within its narrow sphere objects of
natural history and antiquities might be collected, and
duplicates exchanged ; and we are sure that many a
chimney-piece in the district would surrender a tithe of its
curiosities for the public use. Were the British Museum,
and other overflowing collections, to distribute among pro-
vincial museums the numerous duplicates which they possess,
they would gradually pass into the schools, and before a
quarter of a century elapsed, museums would be found in
every proper locality.
As we cannot indulge in the hope that any such boon
1 " The importance of establishing % permanent Museum of Education in this
country, with the view of introducing improvements in the existing methods of
instruction, and specially directing public attention in a practical manner to the
question of National Education, has been of late generally recognised." — Third
Report of the Commissioners for the Exhibition 0/1851, presented to both Houses
of Parliament, p. 37. Lond., 1856.
196 USE OF THE STEREOSCOPE IN EDUCATION. CHAP. Xm.
will be conferred on our educational institutions, it becomes
an important question how far it is possible to supply the
defect by the means within our reach. The photographic
process may be advantageously employed in producing accu-
rate representations of those objects, both of nature and of
art, which it would be desirable to describe and explain in
the instruction of youth ; but as experience has not yet
taught us that such pictures will be permanent, and capable
of resisting the action of time and the elements, it would
be hazardous to employ them in the illustration of popular
works. It is fortunate, however, that the new art of
galvanography enables us, by a cheap process, to give to
photographs the permanence of engravings, and to employ
them in the illustration of educational works. 1
But however much we may value such an auxiliary,
representations or drawings, on a plane, of solids or combi-
nations of solids at different distances from the eye, are in
many cases unintelligible even to persons well informed ; so
that, on this ground alone, we cannot but appreciate the
advantages to be derived from binocular pictures and their
stereoscopic relievo, not only in the instruction of youth,
but in the diffusion of knowledge among all ranks of
society.
One of the most palpable advantages to be derived from
the illustration of school-books by pictures in relief, is the
communication of correct knowledge of the various objects
of natural history. If, as we have already shewn, the na-
turalist derives important assistance in his studies from
i This fine inrention we owe to Mr. Paul Pretsch, late director of the Imperial
Printing Office at Vienna. It is secured by patent, and is now in practical opera-
tion in Holloway Place, Islington.
CHAP. Xm. U8E OP THE STEREOSCOPE IN EDUCATION. 197
correct representations of animated nature, how much more
valuable must they be to the scholar who never saw, and
may never see the objects themselves. In the department
of zoology, the picture might frequently be taken from the
living animal, standing before the camera in vigorous life
and transcendent beauty ; or when this cannot be done, from
the fine specimens of zoological forms which adorn our
metropolitan and provincial museums. The trees and
plants, too, of distant zones, whether naked in their osteo-
logy, or luxurious in their foliage, would shew themselves
in full relief; — the banyan, clinging with its hundred roots
to the ground, — the bread-fruit tree, with its beneficent
burden, — the cow tree, with its wholesome beverage, — the
caoutchouc tree, yielding its valuable juice, — or the deadly
upas, preparing its poison for the arrow of the savage or
the poniard of the assassin.
With no less interest will the schoolboy gaze on the
forms of insect life, which will almost flutter before him,
and on the tenants of the air and of the ocean, defective
only in the colours which adorn them. The structures of
the inorganic world will equally command his admiration.
The minerals which have grown in the earth beneath his
feet, and the crystals which chemistry has conjured into
being, will display to him their geometric forms, infinite in
variety, and interesting from their rarity and value. Painted
by the very light which streamed from them, he will see,
in their retiring and advancing facets, the Kohinoor and
other diamonds, and the huge rubies, and sapphires, and
emeralds, which have adorned the chaplet of beauty, or
sparkled in the diadem of kings. The gigantic productions
of the earth will appeal to him with equal power, — the
198 USE OF THE STEREOSCOPE IN EDUCATION. CHAP. XHL
coloesal granites, which have travelled in chariots of ice,
and the rounded boulders, which have been transported in
torrents of mud; and while he admires, in their strong
relief the precipices of ancient lava — the Doric colonnades
of basalt — the upheaved and contorted strata beside them,
and the undisturbed beds which no internal convulsions
have shaken, he will stand appalled before the fossil giants
of the primeval world that trod the earth during its prepa-
ration for man, and have been embalmed in stone to instruct
and to humble him.
In acquiring a knowledge of physical geography, in which
the grander aspects of nature arrest our attention, their
stereoscopic representations will be particularly instructive.
The mountain range, whether abrupt in its elevation, or
retiring from our view, — whether scarred with peaks or
undulating in outline, — the insulated mountain tipped with
snow or glowing with fire, — the volcano ejecting its burning
missiles, 1 — the iceberg fixed in the shore, or floating on the
deep, — the deafening cataract, — the glacier and its moraines,
sinking gently to the plains, — and even the colossal
wave with its foaming crest, will be portrayed in the
binocular camera, and exhibited in all the grandeur and
life of nature.
The works of human hands, — the structures of civilisa-
tion, will stand before the historian and the antiquary, as
1 An accomplished traveller, the Ber. Mr. Bridges, who ascended Mount Etna
for the purpose of taking Talbotype drawings of its scenery, placed his camera on
the edge of the crater to obtain a representation of it No sooner was the camera
fixed and the senfeitiye paper introduced, than an eruption took place, which
forced Mr. Bridges to quit his camera in order to sare his life. When the eruption
closed, he returned to collect the fragments of his instrument, when, to his great
surprise and delight, he found that his camera was not only uninjured, but con-
tained a picture of the crater and its eruption.
CHAP. Xm. USE OF THE STEREOSCOPE IN EDUCATION. 199
well as the student, in their pristine solidity, or in their
ruined grandeur, — the monuments by which sovereigns and
nations have sought to perpetuate their names, — the
gorgeous palaces of kings, — the garish temples of supersti-
tion, — the humbler edifices of Christian faith, — the bastions
and strongholds of war, will display themselves in the
stereoscope as if the observer were placed at their base,
and warmed by the very sun which shone upon their
walls.
Although few of our village youth may become sculptors,
yet the exhibition of ancient statues in their actual relief,
and real apparent magnitude, cannot fail to give them salu-
tary instruction and rational pleasure. To gaze upon the
Apollo Belvidere, — the Venus de Medici, — the Laocoon,
and the other masterpieces of ancient art, standing in the
very halls which they now occupy; or to see the chef
cToeuvres of Canova, Thorvaldsen, and Ohantrey, or the pro-
ductions of living artists in their own studio, with the
sculptor himself standing by their side, will excite an in-
terest of no ordinary kind.
From the works of the architect, the engineer, and the
mechanist, as exhibited in full relief, the student, whether
at our schools or colleges, will derive the most valuable
instruction. The gigantic aqueducts of ancient and
modern times, — the viaducts and bridges which span our
valleys and our rivers, and the machinery in our arsenals,
factories, and workshops, will be objects of deep interest to
the general as well as the professional inquirer.
There is yet another application of the stereoscope
to educational purposes, not less important than those
which have been mentioned. In the production of diagram
300 U5KOrYHKSmm0©CDFKI5EDCrCiIHHL CXAF.ZmL
if^ g ^riiian g mfinoneats and apparatus, which cannot be
asdentoad from drawings of them on a pisae. it will be of
jacakniahie use to die teacher to hare stereoscopic jirtmrm
of theam. In every hnmeh of physical science, diagiawa of
lids kind art required. When they art huteaded to repre-
sent apparssas and instruments, ether far iDaBtatissj
sjm/*h troths, or caiiiing on physical researches, bouoolar
pictures can be easily obtained ; but when the dJagmm
bare not been taken from apparatus, but ape merely cosa-
hjnariflns of hues, we can oteain binocular photographs of
them only from models constructed cm purpose, These
models will give binocular representations in various
*armTTt->tR t so thai the true positicm of pV"*?*** at tfifiuiwt
inrlinatiom and lines at various angles with eacb other,
and at different distances from the eye. will be readily
apprehended. .Astronomical diacisins, in which orbits, OuC_
may be represented by wires, and optical figures, in which
the rays may be fanned by threads or wires, would be tans
easily executed.
Among the binocular diagrams, consisting of white lines
upon a black ground, which hare been executed in Paris,
there is one representing the apparatus in which a ray of
light, polarised by reflexion from a glass plate, passes
through a crystallised film perpendicular to the plane of
the paper, and is subsequently analysed by reflexion tram
another plate at right angle to the following plate, This
diagram, when placed in relief by the stereoscope, gives as
correct an idea of the process as the apparatus itself
As an auxiliary in the investigation of questions of diflB-
00% and importance, both in physics and metaphysics, the
stereoscope is peculiarly valuable. It enables us to place
CHAP. Xm. USE OF THE STEREOSCOPE IN EDUCATION. 201
in its true light the celebrated theory of vision on which
Bishop Berkeley reared the ideal philosophy, of which he
was the founder, and it gives us powerful aid in explaining
many physical phenomena which have long baffled the inge-
nuity of philosophers. It would be out of place to give any
account of these in a work like this, but there is one so
remarkable, and at the same time so instructive, as to merit
special notice. In order to exhibit, by means of three dia-
grams, a solid in relief and hollow at the same time, which
had not been previously done, I executed three drawings of
the frustum of a cone, resembling those in Fig. 31, so that
the left-hand one and the middle one gave the hollow cone,
while the middle one and the right-hand one gave the raised
cone. Having their summits truncated, as in the figure,
the cones exhibit, in the one case, a circle at the bottom of
the hollow cone, and in the other, a circle on the summit
of the raised cone. When these three diagrams 1 are placed
in an open lenticular stereoscope, or are united by the con-
vergency of the optical axes, so that we can not only see
the hallow and the raised cones, but the flat drawing on
each side of them, we are enabled to give an ocular and
experimental proof of the cause of the large size of the hori-
zontal moon, of her small size when in the meridian or at a
great altitude, and of her intermediate apparent magnitude
at intermediate altitudes, — phenomena which had long per-
plexed astronomers, and which Dr. Berkeley, rejecting pre-
vious and well-founded explanations, ascribed to the different
degrees of brightness of the moon in these different positions.
A binocular slide, copied from the one originally designed by myself, forms
No. 27 of the Series of white-lined diagrams upon a black ground executed in
Paris. The drawings, however, are too large for the common stereosqppe.
202 USE OF THE STEREOSCOPE IN EDUCATION. CHAP. XTTT.
As the circular summit of the raised cone appears to be
nearest the eye of the observer, the summit of the hollow
cone farthest off, and the similar central circle in the flat
drawing on each side, at an intermediate distance, the
apparent distances from the eye of different and equal
circles will represent the apparent distance of the moon in
the zenith, or very high in the elliptical celestial vault, —
the same distance when she is in the horizon, and the same
when' at an intermediate altitude. Being in reality of
exactly the same size, and at the same distance from the
eye, these circular summits, or sections of the cone, are
precisely in the same circumstances as the moon in the
three positions already mentioned. If we now contemplate
them in the lenticular stereoscope, we shall see the circular
summit of the hollow cone the largest, like the horizontal
moon, because it seems to be at the greatest distance from
the eye, — the circular summit of the raised cone the smallest,
because it appears at the least distance, like the zenith or
culminating moon, — and the circular summits of the flat
cones on each side, of an intermediate size, like the moon
at an intermediate altitude, because their distance from
the eye is intermediate. The same effect will be equally
well seen by placing three small wafers of the same size
and colour on the square summits of the drawings of the
quadrangular pyramids, or more simply, by observing the
larger size of the square summit of the hollow pyramid.
This explanation of the cause of the increased size of the
horizontal moon is rigorously correct. If any person should
suspect that the circles which represent the moon are un-
equal in size, or are at different distances from the eye, they
have only to cut the diagram into three parts, and make
CHAP. XTTT. USB OF THE STEBEOSCOPE IN EDUCATION. 203
each drawing of the frustum of the cone occupy a different
place in the binocular slide, and they will obtain the very
same results. Hence we place beyond a doubt the incor-
rectness of Dr. Berkeley's theory of the size of the horizontal
moon, — a theory to which the stereoscope enables us to
apply another test, for if we make one or more of these
circles less bright than the rest, no change whatever will
be produced in their apparent magnitude.
204 USB OF THE STEREOSCOPE FOE AMUSEMENT. CHAP. XIV.
CHAPTER XIV.
APPLICATION OP THE STEREOSCOPE TO PURPOSES OP
AMUSEMENT.
Every experiment in science, and every instrument de-
pending on scientific principles, when employed for the
purpose of amusement, must necessarily be instructive.
" Philosophy in sport" never fails to become " Science in
earnest." The toy which amuses the child will instruct
the sage, and many an eminent discoverer and inventor can
trace the pursuits which immortalize them to some experi-
ment or instrument which amused them at school The
soap bubble, the kite, the balloon, the water wheel, the
sun-dial, the burning-glass, the magnet, &c, have all been
valuable incentives to the study of the sciences.
In a list of about 150 binocular pictures issued by the
London Stereoscopic Company, under the title of " Miscel-
laneous Subjects of the * Wilkie ' character," there are many
of an amusing kind, in which scenes in common life are
admirably represented. Following out the same idea, the
most interesting scenes in our best comedies and tragedies
might be represented with the same distinctness and relief
as if the actors were on the stage. Events and scenes in
ancient and modern history might be similarly exhibited,
and in our day, binocular pictures of trials, congresses,
CHAP. XIV. USE OF THE STEREOSCOPE FOB AMUSEMENT. 205
political, legislative, and religious assemblies, in which the
leading actors were represented, might be provided for the
stereoscope.
For the purpose of amusement, the photographer might
carry us even into the regions of the supernatural. His
art, as I have elsewhere shewn, enables him to give a spiri-
tual appearance to one or more of his figures, and to exhibit
them as " thin air" amid the solid realities of the stereo-
scopic picture. While a party is engaged with their whist
or their gossip, a female figure appears in the midst of them
with all the attributes of the supernatural. Her form is
transparent, every object or person beyond her being seen
in shadowy but distinct outline. She may occupy more
than one place in the scene, and different portions of the
group might be made to gaze upon one or other of the
visions before them. In order to produce such a scene, the
parties which are to compose the group must have their
portraits nearly finished in the binocular camera, in the
attitude which they may be supposed to take, and with
the expression which they may be supposed to assume,
if the vision were real When the party have nearly
sat the proper length of time, the female figure, suit-
ably attired, walks quickly into the place assigned her,
and after standing a few seconds in the proper attitude,
retires quickly, or takes as quickly, a second or even a
third place in the picture if it is required, in each of
which she remains a few seconds, so that her picture in
these different positions may be taken with sufficient dis-
tinctness in the negative photograph. If this operation has
been well performed, all the objects immediately behind the
female figure, having been, previous to her introduction,
USE OF THE STEEEBOOPE FOB AMUSEMENT. CHAP. XIV.
impressed upon the negative surface, will be seen through
her, and she will have the appearance of an aerial personage,
unlike the other figures in the picture. This experiment
may be varied in many ways. One body may be placed
within another, a chicken, for example, within an egg, and
singular effects produced by combining plane pictures with
solid bodies in the arrangement of the persons and things
placed before the binocular camera. Any individual in a
group may appear more than once in the same picture, either
in two or more characters, and no difficulty will be expe-
rienced by the ingenious photographer in giving to these
double or triple portraits, when it is required, the same
appearance as that of the other parties who have not changed
their place. In groups of this kind curious effects might
be produced by placing a second binocular slide between
the principal slide and the eye, and giving it a motion
within the stereoscope. The figures upon it must be
delineated photographically upon a plate of glass, through
which the figures on the principal slide are seen, and the
secondary slide must be so close to the other that the
figures on both may be distinctly visible, if distinct vision
is required for those which are to move.
Another method of making solid figures transparent in a
photograph has been referred to in the preceding chapter, and
may be employed in producing amusing combinations. The
transparency is, in this case, produced by using a large lens,
the margin of which receives the rays which issue from bodies,
or parts of bodies, situated behind other bodies, or parts of
bodies, whose images are given in the photograph. The body
thus rendered transparent must be less in superficial extent
than the lens, and the body seen through it must be so far
CHAP. XIV. USE OF THE STEREOSCOPE FOB AMUSEMENT. 207
behind it that rays emanating from it would fall upon some
part of the lens, the luminosity of this body on the photo-
graph being proportional to the part of the surface of the
lens upon which the rays fall This will be readily under-
stood from Figs. 48 and 49, and their description, and the
ingenious photographer will have no difficulty in producing
very curious effects from this property of large object-glasses.
One of the most interesting applications of the stereo-
scope is in combining binocular pictures, constructed like
the plane picture, used in what has been called the cosmo-
rama for exhibiting dissolving views. These plane pictures
are so constructed, that when we view them by reflected
light, as pictures are generally viewed, we see a particular
scene, such as the Chamber of Deputies in its external
aspect ; but when we allow no light to fall upon it, but
view it by transmitted light, we see the interior of the
building brilliantly lighted up, and the deputies listening
to the debate. In like manner, the one picture may repre-
sent two armies in battle array, while the other may repre-
sent them in action. A cathedral in all its architectural
beauty may be combined with the same building in the act
of being burned to the ground ; or a winter scene covered
with snow may be conjoined with a landscape glowing with
the warmth and verdure of summer. In the cosmorama,
the reflected light which falls upon the front of the one
picture is obtained by opening a lid similar to that of the
stereoscope, as shewn at CD, Fig. 14, while another lid
opening behind the picture stops any light which might
pass through it, and prevents the second picture from being
seen. If, when the first picture is visible, we gradually
open the lid behind it, and close the lid cd before it, it
208 USE OF THE STEBEOSCOPE FOR AMUSEMENT. CHAP. XIV.
gradually disappears, or dissolves, and the second picture
gradually appears till the first vanishes and the second
occupies its place. A great deal of ingenuity is displayed
by the Parisian artists in the composition of these pictures,
and the exhibition of them, either in small portable instru-
ments held in the hand, or placed on the table, or on a
great scale, to an audience, by means of the oxygen and
hydrogen light, never fails to excite admiration.
The pictures thus exhibited, though finely executed, have
only that degree of relief which I have called monocular,
and which depends on correct shading and perspective ;
but when the dissolving views are obtained from binocular
pictures, and have all the high relief given them by their
stereoscopic combination, the effect must be singularly
fine.
Very interesting and amusing effects are produced by
interchanging the right and the left eye pictures in the
stereoscope. In general, what was formerly convex is now
concave, what was round is hollow, and what was near is
distant. The effect of this interchange is finely seen in the
symmetrical diagrams, consisting of white lines upon black
ground, such as Nos. 1, 5, 9, 12, 18 and 27 of the Parisian
set ; but when the diagrams are not symmetrical, that is,
when the one half is not the reflected image of the other,
such as Nos. 26, &c, which are transparent polygonal solids,
formed as it were by white threads or wires, no effect, be-
yond a slight fluttering, is perceived. As the right and
left eye pictures are inseparable when on glass or silver
plate, the experiments must be made by cutting in two the
slides on Bristol board. This, however, is unnecessary
when we have the power of uniting the two pictures by the
CHAP. XIV. USE OF THE STEREOSCOPE FOB AMUSEMENT. 209
convergency of the optic axes to a nearer point, as we
obtain, in this case, the same effect as if we had inter-
changed the pictures. The following are some of the
results obtained in this manner from well-known slides : —
In single portraits no effect is produced by the inter-
change of the right and left eye pictures. If any loose
part of the dress is in the foreground it may be carried
into the distance, and vice versa. In one portrait, the end
of the hat-band, which hung down loosely behind the party,
was made to hang in front of it.
In pictures of streets or valleys, and other objects in
which the foreground is connected with the middle-ground,
and the middle-ground with the distance, without any
break, no effect is produced by the interchange. Some-
times there is a little bulging out of the middle distance,
injurious to the monocular effect.
In the binocular picture of the Bridge of Handeck, the
Chalet in the foreground retires, and the middle distance
above it advances.
In the picture of the sacristy of Notre Dame, the sa-
cristy retires within the cathedral.
In the Maison des Chapiteaux at Pompeii, the picture is
completely inverted, the objects in the distance coming into
the foreground.
In the Daguerreotype of the Crystal Palace, the water
in the foreground, with the floating plants, retires and
takes an inclined position below a horizontal plane.
In the binocular picture of the lower glacier of Rosenlaui,
the roof of the ice-cave becomes hollow, and the whole
foreground is thrown into a disordered perspective.
In Copeland's Venus, the arm holding the bunch of
o
210 USE OF THE STEREOSCOPE FOR AMUSEMENT. CHAP. XIV.
grapes is curiously bent and thrown behind the head,
while the left arm advances before the child.
In the picture of the Greek Court in the Crystal Palace,
the wall behind the statues and columns advances in front
of them.
The singular fallacy in vision which thus takes place is
best seen in a picture where a number of separate articles
are placed upon a table, and in other cases where the
judgment of the spectator is not called upon to resist the
optical effect. Although the nose of the human face should
retire behind the ears yet no such effect is produced, as all
the features of the face are connected with each other, but
if the nose and ears had been represented separately in the
position which they occupy in the human head, the nearer
features would have retired behind the more remote ones,
like the separate articles on a table.
We shall have occasion to resume this subject in our
concluding chapter on the fallacies which take place in
viewing solids, whether raised or hollow, and whether seen
by direct or inverted vision.
CHAP. XV. PRODUCTION OP STEREOSCOPIC PICTURES. 211
CHAPTER XV.
ON THE PRODUCTION OF STEREOSCOPIC PICTURES FROM
A SINGLE PICTURE.
Those who are desirous of having stereoscopic relievos of
absent or deceased Mends, and who possess single photo-
graphic portraits of them, or even oil paintings or miniatures,
will be anxious to know whether or not it is possible to
obtain from one plane picture another which could be com-
bined with it in the stereoscope ; that is, if we consider
the picture as one seen by either eye alone, can we by any
process obtain a second picture as seen by the other eye 9
We have no hesitation in saying that it is impossible to do
this by any direct process.
Every picture, whether taken photographically or by the
eye, is necessarily a picture seen by one eye, or from one
point of sight ; and, therefore, a skilful artist, who fully
understands the principle of the stereoscope, might make
a copy of any picture as seen by the other eye, so approx-
imately correct as to appear in relief when united with the
original in the stereoscope ; but the task would be a very
difficult one, and if well executed, so as to give a relievo
without distortion, the fortune of the painter would be
made.
212 PRODUCTION OF STEREOSCOPIC PICTURES CHAP. XV.
When the artist executes a portrait, he does it from one
point of sight, which we may suppose fixed, and corre-
sponding with that which is seen with his left eye. If
he takes another portrait of the same person, occupying
exactly the same position, from another point of sight,
two and a half inches to the right of himself, as seen with
his right eye, the two pictures will differ only in this, that
each point in the head, and bust, and drapery, will, in the
second picture, be cairied farther to the left of the artist on
the plane of representation. The points which project
most, or are most distant from that plane, will be carried
farther to the left than those which project less, the extent
to which they are carried being proportional to the amount
of their projection, or their distance from the plane. But
since the painter cannot discover from the original or left-
eye plane picture the degree of prominence of the leading
points of the head, the bust, and the drapery, he must
work by guess, and submit his empirical touches, step by
step, to the judgment of the stereoscope. In devoting
himself to this branch of the art he will doubtless acquire
much knowledge and dexterity from experience, and may
succeed to a very considerable extent in obtaining pictures
in relief, if he follows certain rules, which we shall en-
deavour to explain.
If the given portrait, or picture of any kind, is not
of the proper size for the stereoscope, it must be reduced to
that size, by taking a photographic copy of it, from which
the right-eye picture is to be drawn.
In order to diminish the size of the diagram, let us
suppose that the plane on which the portrait is taken
touches the back of the head, and is represented in section
CHAP. XV.
FEOM A SINGLE PICTURE.
213
by ab, Fig. 50. We must now assume, under the guid-
ance of the original, a certain form of the head, whose
breadth from ear to ear is ee", n being the point of the
nose in the horizontal section of the head, e'nen', pass-
ing through the nose n, and the lobes ee" of the two ears.
Let l,r be the left and right eyes of the person viewing
them, and ln the distance at which they are viewed, and
214 PRODUCTION OF STEREOSCOPIC PICTURES CHAP. XV.
let lines be drawn from l and b, through l,n,b and e",
meeting the plane ab on which the portrait is taken in
4, if", n, tf, e, and tf. The breadth, e"V, and the distances
of the nose from the ears n'e', n'e"', being given by
measurement of the photograph suited to the stereoscope,
the distances nn*, ee*, e"e"' may be approximately obtained
from the known form of the human head, either by pro-
jection or calculation. With these data, procured as
correctly as we can, we shall, from the position of the nose
n, as seen by the right eye s, have the formula
_. LBxNN'
* n = HL '
The distance of the right ear e', from the right-eye
picture, will be,
ne 1 = e'N — N*ft; and as He =
LRxEE,
EL
The distance of the left ear e, in the right-eye picture, from
the nose n, will be
ne = n't* + N^ — He.
In order to simplify the diagram we have made the original,
or left-eye picture, a front view, in which the nose is in
the middle of the face, and the line joining the ears parallel
to the plane of the picture.
When the position of the nose and the ears has been
thus approximately obtained, the artist may, in like manner,
determine the place of the pupils of the two eyes, the point
of the chin, the summit of the eyebrows, the prominence
of the lips, and the junction of the nose with the teeth, by
assuming, under the guidance of the original picture, the
distance of these different parts from the plane of projec-
tion. In the same way other leading points in the figure
and drapery may be found, and if these points are deter-
CHAP. XV. FEOM A SINGLE PICTUBE. 215
mined with tolerable accuracy the artist will be able to
draw the features in their new place with such correctness
as to give a good result in the stereoscope.
In drawing the right-eye picture the artist will, of
course, employ as the groundwork of it a faint photo-
graphic impression of the original, or left-eye picture, and
he may, perhaps, derive some advantage from placing the
original, when before the camera, at such an inclination to
the axis of the lens as will produce the same diminution in
the horizontal distance between any two points in the
head, at a mean distance between n and rf, as projected
upon the plane ab. The line iTE" 1 , for example, which in
the left-eye photograph is a representation of the cheek
NE", is reduced, in the right-eye photograph, to n#, and,
therefore, if the photograph on ab, as seen by the right
eye, were placed so obliquely to the axis of the lens that
Hf'e was reduced to nd, the copy obtained in the camera
would have an approximate resemblance to the right-eye
picture required, and might be a better groundwork for the
right-eye picture than an accurate copy of the photograph on
ab, taken when it is perpendicular to the axis of the lens.
In preparing the right-eye picture, the artist, in place of
using paint, might use very dilute solutions of aceto-nitrate
of silver, beginning with the faintest tint, and darkening
these with light till he obtained the desired effect, and,
when necessary, diminishing the shades with solutions of
the hypo-sulphite of soda. When the picture is finished,
and found satisfactory, after examining its relief in the
stereoscope, a negative picture of it should be obtained in
the camera, and positive copies taken, to form, with the ori-
ginal photographs, the pair of binocular portraits required.
216 FALLACIES IK VISION. CHAP. XVI.
CHAPTER XVL
ON CERTAIN FALLACIES OF SIGHT IN THE VISION OF
SOLID BODIES.
In a preceding chapter I have explained a remarkable
fallacy of sight which takes place in the stereoscope when we
interchange the binocular pictures, that is, when we place
the right-eye picture on the left side, and the left-eye
picture on the right side. The objects in the foreground
of the picture are thus thrown into the background, and,
vice versa, the same effect, as we have seen, takes place when
we unite the binocular pictures, in their usual position, by
the ocular stereoscope, that is, by converging the optic
axes to a point between the eye and the pictures. In both
these cases the objects are only the plane representations of
solid bodies, and the change which is produced by their
union is not in their form but in their position. In certain
cases, however, when the object is of some magnitude in
the picture, the form is also changed in consequence of the
inverse position of its parts. That is, the drawings of
objects that are naturally convex will appear concave,
and those which are naturally concave will appear convex.
In these phenomena there is no mental illusion in their
production. The two similar points in each picture, if
they are nearer to one another than other two similar
CHAP. XVL FALLACIES IN VISION. 217
points, must, in conformity with the laws of vision, appear
nearer the eye when combined in the common stereoscope.
When this change of place and form does not appear, as in
the case of the human figure, previously explained, it is by
a mental illusion that the law of vision is controlled.
The phenomena which we are about to describe are, in
several respects, different from those to which we have re-
ferred. They are seen in monocular as well as in binocular
vision, and they are produced in all cases under a mental
illusion, arising either from causes over which we have no .
control, or voluntarily created and maintained by the
observer. The first notice of this class of optical illusion
was given by Aguilonius in his work on optics, to which
we have already had occasion to refer. 1 After proving
that convex and concave surfaces appear plane when seen
at a considerable distance, he shews that the same surfaces,
when seen at a moderate distance, frequently appear what
he calls converse, that is, the concave convex, and the con-
vex concave. This conversion of forms, he says, is often
seen in the globes or balls which are fixed on the walls of
fortifications, and he ascribes the phenomena to the circum-
stance of the mind being imposed upon from not knowing
in what direction the light falls upon the body. He states
that a concavity differs from a convexity only in this re-
spect, that if the shadow is on the same side as that from
which the light comes it is a concavity, and if it is on the
opposite side, it is a convexity. Aguilonius observes also,
that in pictures imitating nature, a similar mistake is com-
mitted as to the form of surfaces. He supposes that a
circle is drawn upon a table and shaded on one side so as
» See Chap. L p. Iff.
218 FALLACIES IN VISION. CHAP. XVI.
to represent a convex or a concave surface. When this
shaded circle is seen at a great distance, it appears a plane
surface, notwithstanding the shadow on one side of it ; but
when we view it at a short distance, and suppose the light
to come from the same side of it as the part not in shadow,
the plane circle will appear to be a convexity, and if we
suppose the light to come from the same side as the shaded
part, the circle will appear to be a concavity.
More than half a century after the time of Aguilonius, a
member of the Royal Society of London, at one of the
meetings of that body, when looking at a guinea through a
compound microscope which inverted the object, was sur-
prised to see the head upon the coin depressed, while other
members were not subject to this illusion.
Dr. Philip Gmelin 1 of Wurtemberg, having learned from
a friend, that when a common seal is viewed through a
compound microscope, the depressed part of the seal appeared
elevated, and the elevated part depressed, obtained the same
result, and found, as Aguilonius did, that the effect was
owing to the inversion of the shadow by the microscope.
One person often saw the phenomena and another did not,
and no effect was produced when a raised object was so
placed between two windows as to be illuminated on all
sides.
In 1780 Mr. Rittenhouse, an American writer, repeated
these experiments with an inverting eye-tube, consisting of
two lenses placed at a distance greater than the sum of
their focal lengths, and he found that when a reflected light
was thrown on a cavity, in a direction opposite to that of
the light which came from his window, the cavity was
i Phil. Trans. 1744.
CHAP. XVI. FALLACIES IN VISION. 219
raised into an elevation by looking through a tube without
any lens. In this experiment the shadow was inverted,
just as if he had looked through his inverting eye-tube.
In studying this subject I observed a number of singular
phenomena, which I have described in my Letters on
Natural Magic, 1 but as they were not seen by binocular
vision I shall mention only some of the more important
facts. If we take one of the intaglio moulds used by the
late Mr. Henning for his bas-reliefs, and direct the eye to
it steadily, without noticing surrounding objects, we may
distinctly see it as a bas-relief. After a little practice I
have succeeded in raising a complete hollow mask of the
human face, the size of life, into a projecting head. This
result is very surprising to those who succeed in the experi-
ment, and it will no doubt be regarded by the sculptor who
can use it as an auxiliary in his art.
Till within the last few years, no phenomenon of this
kind, either as seen with one or with two eyes, had been
noticed by the casual observer. Philosophers alone had
been subject to the illusion, or had subjected others to its
influence. The following case, however, which occurred to
Lady Georgiana Wolff, possesses much interest, as it could
not possibly have been produced by any voluntary effort.
" Lady Georgiana," says Dr. Joseph Wolff in his Journal,
" observed a curious optical deception in the sand, about
the middle of the day, when the sun was strong : all the
footprints, and other marks that are indented in the sand,
had the appearance of being raised out of it. At these
times there was such a glare, that it was unpleasant for the
1 Letter v. pp. 98-107. See also the Edinburgh Journal of Science, Jan. 1826,
vol. iv. p. 99.
MO TAUJlCJSS js veiox. CHAP. XVI.
eye.** 1 Having no doubt of the correctness of this obser-
vation, I have often endeavoured, though in Tain, to wit-
ness so remarkable a phenomenon. In walking, however,
in the month of March last, with a friend on the beach at
St. Andrews, the phenomenon presented itsel£ at the same
instant, to myself and to a lady who was unacquainted
with this class of illusions. The impressions of the feet of
men and of horses were distinctly raised out of the sand. In
a short time they resumed their hoUow form, but at differ-
ent places the phenomenon again presented itseH sometimes
to myself sometimes to the lady, and sometimes to both of
us simultaneously. The sun was near the horizon on our
left hand, and the white surf of the sea was on our right,
strongly reflecting the solar rays. It is very probable that
the illusion arose from our considering the light as coming
from the white surf, in which case the shadows in the
hollow foot-prints were such as could only be produced by
foot-prints raised from the sand, as if they were in relief It
is possible that, when the phenomenon was observed by
Lady Georgian* Wolff, there may have been some source
of direct or reflected light opposite to the sun, or some un-
usual brightness of the clouds, if there were any in that
quarter, which gave rise to the illusion.
When these illusions, whether monocular or binocular,
are produced by an inversion of the shadow, either real or
supposed, they are instantly dissipated by holding a pin in
the field of view, so as to indicate by its shadow the real
place of the illuminating body. The figure will appear
raised or depressed, according to the knowledge which we
obtain of the source of light, by introducing or withdrawing
* JtfttriMU&ft, pas*
CHAP. XVI. FALLACIES IN VISION. 221
the pin. When the inversion is produced by the eye-piece
of a telescope, or a compound microscope, in which the field
of view is necessarily small, we cannot see the illuminating
body and the convex or concave object (the cameo or
intaglio) at the same time ; but if we use a small inverting
telescope, 1£ or 2 inches long, such as that shewn at mn,
Fig. 36, we obtain a large field of view, and may see at
the same time the object and a candle placed beside it. In
this case the illusion will take place according as the candle
is seen beside the object or withdrawn.
If the object is a white tea-cup, or bowl, however large,
and if it is illuminated from behind the observer, the re-
flected image of the window will be in the concave bottom
of the tea-cup, and it will not rise into a convexity if the
illumination from surrounding objects is uniform ; but if
the observer moves a little to one side, so that the reflected
image of the window passes from the centre of the cup,
then the cup will rise into a convexity, when seen through
the inverting telescope, in consequence of the position of
the luminous image, which could occupy its place only upon
a convex surface. If the concave body were cut out of a
piece of chalk, or pure unpolished marble, it would appear
neither convex nor concave, but flat.
Very singular illusions take place, both with one and two
eyes, when the object, whether concave or convex, is a hollow
or an elevation in or upon a limited or extended surface —
that is, whether the surface occupies the whole visible field,
or only a part of it. If we view, through the inverting
telescope or eye-piece, a dimple or a hemispherical cavity in
a broad piece of wood laid horizontally on the table, and
illuminated by quaquavemu light, like that of the sky, it
222 FALLACIES IN VISION. CHAP. XVL
will instantly rise into an elevation, the end of the telescope
or eye-piece resting on the surface of the wood. The change
of form is, therefore, not produced by the inversion of the
shadow, but by another cause. The surface in which the
cavity is made is obviously inverted as well as the cavity,
that is, it now looks downward in place of upward ; but it
does not appear so to the observer leaning upon the table,
and resting the end of his eye-piece upon the wooden surface
in which the cavity is made. The surface seems to him to
remain where it was, and still to look upwards, in place of
looking downwards. If the observer strikes the wooden
surface with the end of the eye-piece, this conviction is
strengthened, and he believes that it is the lower edge of
the field of view, or object-glass, that strikes the apparent
wooden surface or rests upon it, whereas the wooden surface
has been inverted, and optically separated from the lower
edge of the object-glass.
In order to make this plainer, place a pen upon a sheet
of paper with the quill end nearest you, and view it through
the inverting telescope : The quill end will appear farthest
from you, and the paper will not appear inverted. In like
manner, the letters on a printed page are inverted, the
top of each letter being nearest the observer, while the
paper seems to retain its usual place. Now in both these
cases the paper is inverted as well as the quill and the
letters, and in reality the image of the quill and of the pen,
and of the lower end of the letters, is nearest the observer.
Let us next place a tea-cup on its side upon the table, with
its concavity towards the observer, and view it through the
inverting telescope. It will rise into a convexity, the nearer
margin of the cup appearing farther off than the bottom,
CHAP. XVI. FALLACIES IN VISION. 223
If we place a short pen within the cup, measuring as it
were its depth, and having its quill end nearest the ob-
server, the pen will be inverted, in correspondence with the
conversion of the cup into a convexity, the quill end appear-
ing more remote, like the margin of the cup which it
touches, and the feather end next the eye like the summit
of the convex cup on which it rests.
In these experiments, the conversion of the concavity into
a convexity depends on two separate illusions, one of which
springs from the other. The first illusion is the erroneous
conviction that the surface of the table is looking upwards
as usual, whereas it is really inverted ; and the second
illusion, which arises from the first, is, that the nearest
point of the object appears farthest from the eye, whereas
it is nearest to it. All these observations are equally appli-
cable to the vision of. convexities, and hence it follows, that
the conversion of relief, caused by the use of an inverting
eye-piece, is not produced directly by the inversion, but by
an illusion arising from the inversion, in virtue of which we
believe that the remotest side of the convexity is nearer our
eye than the side next us.
In order to demonstrate the correctness of this explana-
tion, let the hemispherical cavity be made in a stripe of
wood, narrower than the field of the inverting telescope with
which it is viewed. It will then appear really inverted,
and free from both the illusions which formerly took place.
The thickness of the stripe of wood is now distinctly seen,
and the inversion of the surface, which now looks downward,
immediately recognised. The edge of the cavity now ap-
pears nearest the eye, as it really is, and the concavity, though
inverted, still appear* a concavity. The same effect is pro-
224 FALLACIES IN VISION. CHAP. XVL
duced when a convexity is placed on a narrow stripe of
wood.
Some curious phenomena take place when we view, at
different degrees of obliquity, a hemispherical cavity raised
into a convexity. At every degree of obliquity from 0° to
90°, that is, from a vertical to a horizontal view of it, the
elliptical margin of the convexity will always be visible,
which is impossible in a real convexity, and the elevated
apex will gradually sink till the elliptical margin becomes
a straight line, and the imaginary convexity completely
levelled. The struggle between truth and error is here so
singular, that while one part of the object has become con-
cave, the other part retains its convexity !
In like manner, when a convexity is seen as a concavity,
the concavity loses its true shape as it is viewed more and
more obliquely, till its remote elliptical margin is en-
croached upon, or eclipsed, by the apex of the convexity ;
and towards an inclination of 90° the concavity disap-
pears altogether, under circumstances analogous to those
already described.
If in place of using an inverting telescope we invert the
concavity, by looking at its inverted image in the focus of
a convex lens, it will sometimes appear a convexity and
sometimes not. In this form of the experiment the image
of the concavity, and consequently its apparent depth, is
greatly diminished, and therefore any trivial cause, such as
a preconception of the mind, or an approximation to a
shadow, or a touch of the concavity by the point of the
finger, will either produce a conversion of form or dis-
sipate the illusion when it is produced.
In the preceding Chapter we have supposed the con-
CHAP. XVI. FALLACIES OF VISION. 225
vexity to be high and the concavity deep and circular, and
we hare supposed them also to be shadowless, or illumi-
nated by a quaquaversus light, such as that of the sky
in the open fields. This was done in order to get rid
of all secondary causes which might interfere with and
modify the normal cause, when the concavities are shal-
low, and the convexities low and have distinct shadows,
or when the concavity, as in seals, has the shape of an
animal or any body which we are accustomed to see in
relief.
Let us now suppose that a strong shadow is thrown
upon the concavity. In this case the normal experiment
is much more perfect and satisfactory. The illusion is
complete and invariable when the concavity is in or
upon an extended surface, and it as invariably disap-
pears, or rather is not produced, when it is in a narrow
stripe.
In the secondary forms of the experiment, the inversion
of the shadow becomes the principal cause of the illusion ;
but in order that the result may be invariable, or nearly
so, the concavities must be shallow and the convexities
but slightly raised. At great obliquities, however, this
cause of the conversion of form ceases to produce the
illusion, and in varying the inclination from 0° to 90°
the cessation takes place sooner with deep than with
shallow cavities. The reason of this is that the shadow of
a concavity is very different at great obliquities from the
shadow of a convexity. The shadow never can emerge
out of a cavity so as to darken the surface in which the
cavity is made, whereas the shadow of a convexity soon
extends beyond the outline of its base, and finally throws
FALLACIES OF VISION. CHAP. XVI.
a long stripe of darkness over the surface on which
it rests. Hence it is impossible to mistake a con-
vexity for a concavity when its shadow extends beyond
its base.
When the concavity upon a seal is a horse, or any other
animal, it will often rise into a convexity when seen through
a single lens, which does not invert it ; but the illusion
disappears at great obliquities. In this case, the illusion
is favoured or produced by two causes ; the first is, that the
form of the horse or other animal in relief is the one
which the mind is most disposed to seize, and the second
is, that we use only one eye, with which we cannot measure
depths as well as with two. The illusion, however, still
takes place when we employ a lens three or more inches
wide, so as to permit the use of both eyes, but it is less
certain, as the binocular vision enables us in some degree
to keep in check the other causes of illusion.
The influence of these secondary causes is strikingly dis-
played in the following experiment. In the armorial
bearings upon a seal, the shield is often more deeply cut
than the surrounding parts. With binocular vision, the
shallow parts rise into relief sooner than the shield, and
continue so while the shield remains depressed ; but if we
shut one eye the shield then rises into relief like the rest.
In these experiments with a single lens a slight variation
in the position of the seal, or a slight change in the inten-
sity or direction of the illumination, or particular reflexions
from the interior of the stone, if it is transparent, will
favour or oppose the illusion. In viewing the shield at
the deepest portion with a single lens, a slight rotation
of the seal round the wrist, backwards and forwards, will
CHAP. XVI. FALLACIES OP VISION. 227
remove the illusion, in consequence of the eye perceiving
that the change in the perspective is different from what
it ought to be.
In my Letters on Natural Magic, I have described
several cases of the conversion of form in which inverted
vision is not employed. Hollows in mother-of-pearl and
other semi-transparent bodies often rise into relief, in con-
sequence of a quantity of light, occasioned by refraction,
appearing on the side next the light, where there should
have been a shadow in the case of a depression. Similar
illusions take place in certain pieces of polished wood, cal-
cedony, mother-of-pearl, and other shells, where the surface
is perfectly plane. This arises from there being at that place
a knot, or growth, or nodule, differing in transparency from
the surrounding mass. The thin edge of the knot, &c,
opposite the candle, is illuminated by refracted light, so
that it takes the appearance of a concavity. From the
same cause arises the appearance of dimples in certain
plates of calcedony, which have received the name of
hammered calcedony, or agate, from their having the look
of being dimpled with a hammer. The surface on which
these cavities are seen contains sections of small spherical
formations of siliceous matter, which exhibit the same illu-
sion as the cavities in wood. Mother-of-pearl presents
similar phenomena, and so common are they in this
substance that it is difficult to find a mother-of-pearl button
or counter which seems to have its surface flat, although it
is perfectly so when examined by the touch. Owing to
the different refractions of the incident light by the dif-
ferent growths of the shell, cut in different directions by
the artificial surface, like the annual growth of wood in a
228 FALLACIES OF VISION. CHAP. XVL
dressed plank, the surface of the mineral has necessarily an
inequai and undulating appearance.
In viewing good photographic or well-painted miniature
portraits in an erect and inverted position, and with or with-
out a lens, considerable changes take place in the apparent
relief Under ordinary vision there is a certain amount of
relief depending upon the excellence of the picture. If we
invert the picture, by turning it upside down, the relief is
perceptibly increased. If we view it when erect, with a
lens of about an inch in focal length, the relief is still
greater ; but if we view it when inverted with the same
lens the relief is very considerably diminished.
A very remarkable illusion, affecting the apparent posi-
tion of the drawings of geometrical solids, was first ob-
served by the late Professor Neckar, of Geneva, who com-
municated it to me personally in 1832. 1 " The rhom-
boid ax," (Fig. 51,) he says, " is drawn so that the solid
Fro. 51.
angle a should be seen nearest to the spectator, and the
solid angle z the farthest from him, and that the face acbd
should be the foremost, while the face xdc is behind. But
1 See Edinburgh Philosophical Journal, Noyember 1832, roL L p. 334
CHAP. XVI. FALLACIES OP VISION. 229
in looking repeatedly at the same figure, you will perceive
that at times the apparent position of the rhomboid is so
changed that the solid angle x will appear the nearest,
and the solid angle a the farthest, and that the face acdb
will recede behind the face xdc, which will come forward,
— which effect gives to the whole solid a quite contrary
apparent inclination." Professor Neckar observed this
change " as well with one as with both eyes," and he con-
sidered it as owing " to an involuntary change in the
adjustment of the eye for obtaining distinct vision. And
that whenever the point of distinct vision on the retina was
directed to the angle a for instance, this angle, seen more
distinctly than the other, was naturally supposed to be
nearer and foremost, while the other angles, seen indis-
tinctly, were supposed to be farther away and behind.
The reverse took place when the point of distinct vision
was brought to bear upon the angle x. What I have said of
the solid angles (a and x) is equally true of the edges,
those edges upon which the axis of the eye, or the central
hole of the retina, are directed, will always appear forward ;
so that now it seems to me certain that this little, at first
so puzzling, phenomenon depends upon the law of distinct
vision."
In consequence of completely misunderstanding Mr.
Neckar' s explanation of this illusion, Mr. Wheatstone has
pronounced it to be erroneous, but there can be no doubt
of its correctness ; and there are various experiments by
which the principle may be illustrated. By hiding with
the finger one of the solid angles, or making it indistinct,
by a piece of dimmed glass, or throwing a slight shadow
over it, the other will appear foremost till the obscuring
230 FALLACIES OF VISION. CHAP. XVL
cause is removed. The experiment may be still more
satisfactorily made by holding above the rhomboid a piece
of finely-ground glass, the ground side being farthest from
the eye, and bringing one edge of it gradually down till it
touches the point a, the other edge being kept at a distance
from the paper. In this way all the lines diverging from
a will become dimmer as they recede from a, and con-
sequently a will appear the most forward point. A
similar result will be obtained by putting a black spot
upon a, which will have the effect of drawing our atten-
tion to a rather than to x.
From these experiments and observations, it will be seen
that the conversion of form, excepting in the normal case,
depends upon various causes, which are influential only
under particular conditions, such as the depth of the
hollow or the height of the relief, the distance of the
object, the sharpness of vision, the use of one or both
eyes, the inversion of the shadow, the nature of the object,
and the means used by the mind itself to produce the
illusion. In the normal case, where the cavity or con-
vexity is shadowless, and upon an extended surface, and
where inverted vision is used, the conversion depends solely
on the illusion, which it is impossible to resist, that the
side of the cavity or elevation next the eye is actually
farthest from it, an illusion not produced by inversion, but
by a false judgment respecting the position of the surface
in which the cavity is made, or upon which it rests.
CHAP. XVH. DIFFICULTY IN USING THE STEREOSCOPE. 231
CHAPTER XVII.
ON CERTAIN DIFFICULTIES EXPERIENCED IN THE USE OF
THE STEREOSCOPE.
There are many persons who experience great difficulty
in uniting the two pictures in the stereoscope, and conse-
quently in seeing the relief produced by their union. If
the eyes are not equal in focal length, that is, in the dis-
tance at which they see objects most distinctly ; or if, from
some defect in structure, they are not equally good, they
will still see the stereoscopic relief, though the picture will
be less vivid and distinct than if the eyes were in every
respect equal and good. There are many persons, however,
whose eyes are equal and perfect, but who are not able to
unite the pictures in the stereoscope. This is the more
remarkable, as children of four or five years of age see the
stereoscopic effect when the eye-tubes are accommodated to
the distance between their eyes. The difficulty experienced
in uniting the binocular pictures is sometimes only tem-
porary. On first looking into the instrument, two pictures
are seen in place of one ; but by a little perseverance, and
by drawing the eyes away from the eye-tubes, and still
looking through them, the object is seen single and in per-
fect relief. After having ceased to use the instrument for
232 DIFFICULTY IN USING THE STEREOSCOPE. CHAP. XVIL
some time, the difficulty of uniting the pictures recurs, but,
generally speaking, it will gradually disappear.
In those cases where it cannot be overcome by repeated
trials, it must arise either from the distance between the
lenses being greater or less than the distance between the
CHAP. XVH. DIFFICULTY IN USING THE STEREOSCOPE.
eyes, or from some peculiarity in the power of converging
the optical axes, which it is not easy to explain.
If the distance between the pupils of the two eyes, e, e',
Fig. 52, which has been already explained on Fig. 18, is
less than the distance between the semi-lenses l, l', then,
instead of looking through the middle portions no, n'o', of
the lenses, the observer will look through portions between
o and l, and o' and l', which have a greater power of re-
fracting or displacing the pictures than the portions no, n' d,
and therefore the pictures will be too much displaced, and
will have so far overpassed one another that the observer is
not able to bring them bach to their place of union, half-
way between the two pictures in the slide.
If, on the other hand, the distance between the pupils of
the observer's eyes is greater than the distance between the
semi-lenses l, l', then, instead of looking through the por-
tions no,n'd of the lenses, the observer will look through
portions between n and l, and n' and l', which have a less
power of refracting or displacing the pictures than the por-
tions no, n'o', and therefore the pictures will be so little
displaced as not to reach their place of union, and will
stand at such a distance that the observer is not able to
bring them up to their proper place, half-way between the
two pictures in the slide.
Now, in both these cases of over and under displacement,
many persons have such a power over their optical axes,
that by converging them to a point nearer than the picture,
they would, in the first case, bring them back to their place
of union, and by converging them to a point more remote
than the picture, would, in the second case, bring them up
to their place of union ; but others are very defective in
234 DIFFICULTY IN USING THE STEREOSCOPE. CHAP. XVIL
this power of convergence, some having a facility of converg-
ing them beyond the pictures, and others between the pic-
tures and 'the eye. This last, however, namely, that of
near convergence, is by far the most common, especially
among men ; but it is of no avail, and the exercise of it is
injurious when the under refracted pictures have not come
up to their place of union. The power of remote converg-
ence, which is very rare, and which would assist in bringing
back the over refracted pictures to their place of union, is
of no avail, and the exercise of it is injurious when the
pictures have been too much displaced, and made to pass
beyond their place of union.
When the stereoscope is perfectly adapted to the eyes of
the observer, and the general union of the pictures effected,
the remote parts of the picture, that is, the objects seen in
the distance, may be under refracted, while those in the
foreground are over refracted, so that while eyes which
have the power of convergence beyond the picture, unite
the more distant objects which are under refracted, they
experience much difficulty in uniting those in the foreground
which are over refracted. In like manner, eyes which have
the power of near convergence will readily unite objects in
the foreground which are over refracted, while they expe-
rience much difficulty in uniting objects in the distance
which are under refracted. If the requisite power over
the optical axes is not acquired by experience and persever-
ance, when the stereoscope is suited to the eyes of the
observer, the only suggestion which we can make is to
open the eyes wide, and expand the eyebrows, which we do
in staring at an object, or in looking at a distant one, when
we wish to converge the axes, as in Fig. 22, to a point
CHAP. XVII. DIFFICULTY IN USING THE STEREOSCOPE. 235
beyond the pictures, and to contract the eyes and the eye-
brows, which we do in too much light, in looking at a near
object, when we wish to converge the optic axes, as in Fig.
21, to a point between the pictures and the eye.
When the binocular pictures are taken at too great an
angle, so as to produce a startling amount of relief, the
distance between similar points in each picture, both in the
distance and in the foreground, is much greater than it
ought to be, and hence the difficulty of uniting the pictures
is greatly increased, so that persons who would have expe-
rienced no difficulty in uniting them, had they been taken
at the proper angle, will fail altogether in bringing them
into stereoscopic relief.
In these observations, it is understood that the observer
obtains distinct vision of the pictures in the stereoscope,
either by the adjustment of the moveable eye-tubes, if they
are moveable, as they ought to be, or by the aid of convex
or concave glasses for both eyes, either in the form of
spectacles, or separate lenses placed immediately above, or
immediately below the semi-lenses in the eye tubes. If the
eyes have different focal lengths, which is not unfrequently
the case, lenses differing in convexity or concavity should
be employed to equalize them.
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" Wonderful instrument." — Times.
" Administers at once to wonder and delight."— Spectator.
THE CRYSTAL PALACE, SYDENHAM,
Shewing the various Courts and points of greatest interest, ivith descriptive
Utter-press at the back of each slide.
The following are mounted on Card, at 3s. each Slide, and are of the
choicest description.
1. The Byzantine Court— interior
View, with the black marble fountain (an
exact copy of one at lieisterbach on the
Rhine), and the celebrated effigies of Henry
II. and his queen Eleanora, and of Isabella,
wife of King John, from Fontevrault Abbey.
2. The Egyptian Court— Entrance
to, with Avenue of Lions. The different styleti
of columns, &c, during the Ptolemaic period,
about 300 years B.C., and the outlines in
low relief on the walls are beautifully de-
lineated.
3. The Court of the Lions-One of
the most gorgeous in the Alhambra, re-
markable for its graceful fretwork and the
fairy-like slightness of ita columns. It de-
rives its name from the stone fountain seen
in its centre, surrounded by lions.
4. The Italian. Court— From a por-
tion of the FarnosePalace at Rome, with the
figure of Lorenzo de' Medici, and Dawn and
Twilight, from the celebrated monument in
the Church of San Lorenzo at Florence.
5. The Pompeian Court— A well-
chosen view from that beautiful Court, being
an actual representation of the " Atrium,"
or hall of a Roman mansion, with its " ira-
pluvium" at the time of the great eruption,
A.D. 79.
6. The Renaissance Court— A cor-
rect epitome of thatarchitecture which super-
seded the florid Gothic of the 15th century,
and returning to a chaster style, is now
known as the renaissance.
7. The Two Colossal Statues— Of
Barneses, from the Temple of Abou Simboul,
in Nubia, sculptured in the solid rock. From
hieroglyphics in the interior the date of
their construction is ascertained to have
been 1560 B.C.
8. The Elizabethan Court— Both
facade and arcades of which are from Hol-
land House, Kensington, together with two
bronze figures by Landini, from the Tarta-
rughe fountain at Rome, and busts of Shake-
speare, &c.
9. Entrance to English Me-
diaeval Court — Showing the western
doorway of Tintern Abbey, and the two
statues from the west front of Wells Cathe-
dral. The celebrated Walsingham font is
seen within the Court.
*lO. The Egyptian Hall of Co-
lumns—This hall exhibits a combination of
columns from various buildings ; some from
the Tomb of Ozymandias, and others crowned
with the head of Athor, the Egyptian Venus.
11. The Telescope Gallery— So
named from the curious effect produced by
its apparently interminable repetition of
rings, when seen from either extremity.
12. The Assyrian Court— With re-
presentations of the hnman-headed bulls
which formed the entrance to the palace at
Khorsabad, and of some of the figures on its
walls, as also of the Sphinxes, cast from one
in the Louvre, dated 1000 years before Christ.
18. View in the Greek Court-
Containing some of the finest examples of
Greek sculpture ; a portion of the Egyptian
Court is also visible, with one of the figures
of Amenoph, restored from the black granite
statue in the British Museum.
14. Entrance to the Egyptian
Court — Remarkable for the dedication on
the frieze, to the Queen, as the " Ruler of the
Waves, the Royal Daughter Victoria, Lady
Most Gracious," &c^ in hieroglyphics.
16. Interior View of the Crystal
Palaoe — Looking towards the north end,
and comprising nearly the whole length of
the nave. Osier's crystal fountain occupies
the centre of the foreground, surrounded by
the colossal statues of Leasing and Hus-
kisson, Lord Chatham, and Dr. Johnson.
16. The Stationery Court— This
View comprises three life-like figures by
Ranch of Berlin, pupil both of Canova and
Thorwaldson. The character of the Court is
composite, with cinque-cento ornamentation.
17* Gallery of Greek Sculpture—
The statues seen in this view are of different
periods of Greek art, but all of the highest
class, from the collections at Rome, Naples,
I Paris, and Berlin.
18. Gallery of Greek Sculpture—
A continuation of the preceding, and com'
prising statues and busts in no way inferior
to it in any of the qualities of high and re-
I fined art.
19. Gallery of Greek Sculpture-
Remarkable principally for the authenticated
busts of Numa Pompilius, and various Roman
Emperors, clustered round the termination
of the gallery looking towards the Court of
the Lions.
20. Gallery of Greek Sculpture—
I Amongst the statues in this continuation of
the Greek Court, is the far-famed Venus de'
Medici, and it is remarkable for the massive
antae or square columns, in the recess between
which is a small statue of Euripides.
21. The Byzantine Court— Two
arches of the arcade from the cloisters of
St. Mary in Capitolo, an ancient church of
Cologne, with examples on the spandrils of
the costume and style of the Byzantine
period, and recumbent figures of the Earl*
of Pembroke and Essex.
22. The Byzantine Court— A con-
tinuation of the same facade, with portraits
of the Emperor Nicephorus, and of Theo-
dora, wife of Justinian.
23. The Italian Court -^Con-
structed after the model of the Farneae
Palace with the statue of Guliano de' Medici,
and the figures of Light and Night, from San
Lorenzo, Florence. In the centre is seen
the fountain of the Tartarughe, from Rome.
24. The Italian Court— The ori-
ginal design of the Farnese Palace, the
model from which this court is taken, was
by Sangallo, but it was completed under the
direction of Michael Angalo; by whom is
the celebrated statue of BacchuB, seen in
front of the facade.
25. English Mediaeval Court-
Part of which is from Tintern Abbey, and
part from Gainsborough, Yorkshire, with
statues from Romsey and Wells Cathedral.
26. Entrance to the Greek
Court — Presenting two columns from the
Temple of Jupiter, at Nemea, and in the
back ground a model, about one-fourth the
size of the original, of the Parthenon, with
antique statuary in the foreground.
27. Interior of Greek Court-
Supported by pillars from the Temple of
Jupiter, at Nemea, constructed about 400
years B.C. Here are the two famous s tatues,
the gladiator Repellens, and the Scythian
whetting his knife.
2a Mixed Fabrics Court— In the
occupation of Sowerby, of Regent Street ; at
this angle is seen Bailey's Graces, and the
Musidora by Thomas.
29. The Roman Court — Nothing
can be more chaste and simple than this
court, its arches rising between Iouic pillars
and separated by a pilaster of the same
order, in harmony with the sculpture it con-
tains.
30. The Statues of Amenoph—
Restored from the original in black granite,
now in the British Museum, together with a
portrait of Rameses II. sitting under the
Persea tree, sculptured on the walls.
31. Interior of English Mediae-
val Court— Most conspicuous in the cen-
tre of this court, is the tomb of Edward the
Black Prince, from Canterbury Cathedral,
and that of William of Wykeham, from Win-
chester, beyond which is the Walsingham
Font.
32. Middle Entrance to the
Greek Court — Showing a Doric column,
part of the facade from the Temple of
Jupiter, at Nemea.
83. Entrance to the Alhambra
Court— An exact fac-simile of the en-
trance into the court of the Lions from the
Court of the Fish-pond. The diaper pattern
on the walls being from the Sala de la Barca.
34. The Nave — Osier's well-known
fountain, Una and the Lion, and the Eagle
Slayer, ate here seen in a line across the
Nave, beyond which are the statues of
Charles I. and James II.
86. Screen of the Kings and
Queens Of England— A beautiful re-
presentation of the Screen designed by M.D.
Wyatt, with the sculpture by Thomas; it is
taken from the angle where the Norman
series commences, and comprises the statue
of her present Majesty.
36. The Tfoftloat Instrument
Court— A truthful representation of the
entrance of this beautiful Court, designed by
Thomas, with a representation of Miriam in
the space above, and a bust of Jubal to the
right.
37. View in the Nave— This view is
taken directly across the Nave, in aline with
Osier's fountain and the statues of Charles
I. and James II.; and showing a line of
statues, by Theed and Gibson, amongst
which most conspicuous is that of Humphrey
Chetham, of Manchester.
38. Group of Africans— Contrast-
ing the Negro of the lower levels, with the
Danakil of the high pastures and plateaus
of jthe Desert.
39. Byzantine Court— Showing the
centre arch of the facade from the Church of
St. Mary in Capitolo, at Cologne, the columns
from which it springs being ornamented with
Capitols of different designs.
40. Mixed Fabrics Court— The
only statue visible from this point of view, is
from the Murder of the Innocents, but it
derives its interest from the tropical ever-
greens, by which it is surrounded.
41. Ceremony of Inauguration
— Being a correct representation taken upon
the spot on the 10th of June, 1854, when Mr.
Laing, the Chairman of the Crystal Palace
Company, was in the act of reading the
address to Her Majesty.
42. Mixed Fabrics Court— Show-
ing the Tired Hunter, a statue by Bailey,
and Apollo discharging his bow, by the
same artist.
43. General View of the Crystal
Palace— A beautiful view of the building
seen from a distance. It is taken from a
point above Anerley station, where it it
seen to the greatest advantage.
44. Portion of the North Wing—
In which the general character of the Italian
Terraces with the vases, statues, flower-beds,
fish-ponds, &c., is seen in connection with a
portion of the building.
46. General View in the Grounds
— As seen from the central corridor, compri-
sing the broad walk down to the great foun-
tain, the village and church, beyond the
grounds, and the hills and variegated land-
scape in the far distance.
The Second Series of about 200
subjects taken from the Crystal
Palace, in addition to and in-
cluding many of the above, with-
out description, mounted at 2s.
each slide.
MISCELLANEOUS SUBJECTS.
Groups, Figures, &e. &c.
FIRST SERIES.
Consisting of numerous Groups and Views,
of an amusing and entertaining character,
of the very finest quality. On card, mounted
at 8s. each slide.
Return from Shooting.
Dead Game.
( 'ock and Fox.
The old Larder.
The Family Torment.
The Egg Girl.
A Dajrs 8port (Group of Fish).
Articles of Vertu.
The Curiosity Shop.
The Enraged Cockatoo; or, a Chinese Ball
in Danger.
The Pet Bird.
Mortality.
Several exquisite Rustic Scenes from Berkshire.
Now Publishing, by permission, some Beautiful Scenes from the
Winter's Tale.
SECOND SERIES.
Hawk and Duckling.
Hen and Weasel.
Group of Four Chinese.
Group of Two Esquimeanz.
Root. Drummond, Valet to late Lord Nelson.
Mr. Lovejoy— objects to being disturbed just
when ho begins to feel comfortable.
(Taken by Command of Her Majesty.)
Group of Three Sailors — Crimean Heroes.
„ Five Royal Marines „
„ 2 Royal Marine Artillery „
Group of 3 Rifle Brigade— Crimean Heroes.
„ 3 Fusilier Guards „
Launch of the Marlborough at Portsmouth.
Ditto another View
Ditto another View.
Very popular Subjects, mounted at 2s. 6d.
each slide.
The Murder of Abel.
Miss Wyndham of the Adelphi, as Columbine.
Qal Masque" (Eighteen Plates).
Mother Goose.
The Emperor and Empress of China.
Roman Woman at the Well.
Crossing the Brook.
Oharity School.
Girl with Fawn (Three Plates).
" Strictly Confidential."
Going to the Ball.
The Coquette.
Boys Blowing Bubbles (Two Plates).
Boys at Play.
Impudence.
Children Swinging.
Dinner Party (Four Plates), group of 8.
Tea Party (Four Plates).
Dessert
Group of Fruit.
Catholic Devotion.
Dancing Figure.
Spanish Dancers (Bight varied Plates).
Clara Novello.
Albert Smith.
Love.
Holmes, or Dead Guy.
Ross, Her Majesty's Piper.
Death of Thomas A'Beoket (Two Plates), to be followed by a complete
Series of Historical Subjects of the deepest interest, with explanatory
letter-press at. back.
Lady Asleep ; Another overlooking.
Lady Reading ; Another overlooking (Two
Plates).
Dead Game.
Costermonger with Game.
Flower Girl.
Fruit Girl.
Fish Girl (Two Plates).
The Gleaner (Two Plates).
Vivandle>e.
Combat (Mr. Albert Smith and Mr. Holmes).
Pantomimes, various and amusing.
Harlequin, Pantaloon, and Columbine.
The Gipsey.
The Toilet.
The Rabbit on the Wall.
Taking a Sight.
Scenes from the Ballet of " Ondine."
" Happy to take Wine withYou." (Group of 7.)
The Tired Gleaner (Two Plates).
Group of Shells.
Mrs. Caudle's Curtain Lecture.
Mr. Caudle's attempt at Peace.
His Success.
The Wedding at St. George's, No. 1.
Baby asleep in Cot, No. 2.
Blind Man*s Buff.
The Christening, No. 3.
Lady at Toilet Glass.
And several other beautiful subjects.
THIRD SERD38.
Miscellaneous Subjects of the " Wilkie" character, very popular, mounted at
Is. 6d. each.
Man and Woman in Yard— Snow Scene.
Ladies seated outside Lodge-door.
Maid taking Joint from Butcher Boy.
Lady seated at Table.
Family Group at Tea.
Do. do., with Eagle.
Conversing with Neighbours over the Wall.
A Boy's School.
Group of Anglers.
Child seen through Anti-Macassar.
Porters gossipping in Yard.
Group round Fish Pond.
Group seated on Garden Chair.
Wooden-legged Man at Kenilworth Castle.
Family Group in Garden.
Interior of Larder.
Ruined Gateway, Kenilworth.
Harrowing Machine.
Militia Men at Skittles.
Porters with Luggage, &c.— Snow 8cene.
Family outside Conservatory.
Group of Game, &c
Men with Truck.
Militia Men under Drill (several Plates).
Poultry larder.
Group of 25 Ladies and Children.
Group of Anglers and Lady.
Family Group in Arbour.
Ladies playing at Chess.
Family Group at and under Window.
Do. do., in Garden.
Group of Labourers.
Boy on Rocking Horse.
Girl on do.
Man weighing out Coals.
Peacock in Garden.
Group of Stuffed Birds in Cases.
Smoking Cigar in Grotto,
Group of Gentlemen at Boat-house.
Gardener sweeping Lawn.
Piece of Ruined Castle covered with Ivy.
Family Group at Cottage Door.
Sportsman Firing ; Gardener and Boy.
Labourers taking their Meals.
Labourers and Shoe-black.
Black Letter and Spectacles.
Packing Soda-water.
Friendly Visit.
Girls giving the Gardener some Porter.
Man washing Dog-cart.
Boys in Punt, Angling.
Blacksmiths.
Gardener Hoeing.
Recruiting party.
Party playing at Skittles.
Bird.
Family in Summer-house.
Soldiers at Cards.
i and Child in Garden.
Child seen through Netting.
Family in Garden.
Group of Ducks, &c
Sportsman ; Child and Labourer in Yard
Sportsman and Family in Garden.
Labourers at Meals.
Family Group.
Gentleman climbing Tree.
Family Group in Garden.
Father nursing Child.
Group round Fish Pond.
Haymaking Machine.
Family Group in Garden.
Labelling Cask.
Meditation.
Papa's Pet in Tree.
Ladies Conversing.
Gentleman in Conservatory.
Gardener gossipping with Maid.
Soldiers playing at Cards.
Coachman talking to Lodge Keeper.
Family Group.
Carmen and Housewife.
" Any Brooms or Brushes?" &c.
Sportsman, Angler, and Friend.
Gentleman at Gate talking to the Carpenter.
Family Group outside Conservatory.
Dustmen and Boys in Yard.
Garden Scene.
Gentlemen at Kenilworth Gateway.
Group of Surveyors.
Family Group.
Lady and Children.
Porters in Yard.
Group of Soldiers.
Porters and Boy in Yard.
Group around Fish Pond.
Mamma and Daughters.
Soldiers on Drill.
Militia Man and Boy on Ladder.
Family at Window and in Garden.
A Solitary Bird.
Large Party of Ladies in Garden.
Lady and Gentlemen in Garden.
Ladies and Children at Door.
Family Group in Garden.
Man and Labourers clearing away Snow.
Labourers loading Truck.
Carpenter, Labourers, and Man offering
Beer.
Playing at Skittles.
Men with Truck, and Boy drinking Le-
monade.
Quaker's Meeting.
Man tying Vine.
Winning the Gloves.
Skull and Spectacles.
( School Boys in Playground.
Piece of Coral (very striking).
Militia Man calls on Mary.
Boy listening to them.
Militia Man gets indignant and knocks down
the Boy.
An old Man interferes.
Mary makes peace.
Departure of the Militia Man.
Gentlemen and Boy in Summer-house.
Militia Man and Porter at Door. (5)
Dog and Kennel.
Gardener and Boy.
" rpenter, Porter, and Boy.
litia Kneeling.
Portion of Ruins, Kenil worth.
Group of Soldiers.
Family Group in Garden.
A Bird.
Shakespeare's House.
Family Group in Garden.
Group of Children in Garden.
Fortune-teller.
Young Lady with Hoop; Servant, cleaning
Window.
Ladies and Maid on Door-steps.
Ruins of Covent Garden Theatre (6 Plates).
Old Patriarch.
Carpeni
Militia
All the Paper Subjects can be bad, exquisitely coloured, at 6d. per Slide,
additional.
Fresh Subjects are continually being added to this class.
A large collection of Daguerreotype Statuary, taken from the orginal marble,
5s. 6d. each.
The same Subjects on paper, Is. 6d. each, including —
Bust of Ariadne by Bacon.
Dorothea by Bell.
Golden Age by Beattie.
Ino and Bacchus by Foley.
Two Cupids struggling for a Heart by
Posschini.
Uncle Toby, Widow Wadman.
Sabrina by Bailey.
Andromeda by Pradier.
Leda and the Swan „
Diana „
Priestess Bacchus „
Greek Slave by Power.
Laocoon from the original statue at Rome.
LANDSCAPES.
SWITZERLAND, WALES, SCOTLAND, ISLE OF WIGHT, JERSEY,
and the choicest Spots in England, including the following Subjects,
from Is. 6d. to 2s. each.
Salisbury Cathedral and its Vicinity.
Shakespeare's House at Stratford-on-Avon.
Do. Tomb.
Anne Hathaway's Cottage.
8tratford-on-Avon Church.
Man in Stocks in Stratford Churchyard.
The Banquet Hall, Kenilworth Castle.
The Mill, Guy's Cliff; Warwick.
The Avenue, ,, „
Leamington College.
Warwick Castle.
Stone Cross in Ashow Churchyard, near
Leamington.
Leicester Buildings, Kenilworth Castle.
Caesar's Tower, „ „
Fire Place in Banquet Hall, „ „
Entrance to Gate House, „ „
Ashow Church, near Leamington.
Stoneleigh Bridge, over the Avon, near
Warwick.
Several choice Views at Hampton Court.
Quarr Abbey.
Egypt, West Cowes.
Shanklin Church.
„ Chine.
„ Dell.
Areton Church.
Binstead Parsonage.
St. Helens.
Chale Church.
Crab Inn.
Skeleton Flowers (very striking).
Charming View near Leamington.
Avenue of Trees at Leamington.
Several beautiful Views of Kenilworth Castle.
With many others.
Fifty varied Stereoscopic Plates of the-
Great Crumlin Viaduct in Wales. This via-
duct is upwards of 200 feet in height, 1750 ■
in length, a most interesting subject for
architects, civil engineers, &c
Various Views of Edinburgh. Aberdeen, &o.
Together with numerous similar Subjects.
In addition to the above, there is a large/
selection of French views, comprising every
subject of interest, including Notre Dame,
Place de la Concorde, Champs Elysees, Place
des Victoires, The Madelaine, The Bourse,
&c, &c , from 9d. to Is. 6d. each ; also,
French and Italian views, of a very superior
quality, mounted at 2s. 6<L each.
POMPEII AND NAPLES.
The following Views comprehend all the principal features and points of
interest, mounted on card at Is. 6d. each slide.
The King of Naples has prohibited the taking of any more Photographic
pictures of Pompeii.
Temple of Serapis at Naples.
Temple of Ceres (No. 1) at Poestum.
Left of the Forum at Pompeii.
The Musician's House at Pompeii.
Temple of Diana at Bala, Naples.
Soldier's Quarters at Pompeii.
Mount Pelegrino, Palermo.
Entrance of the Forum at Pompeii.
Entrance of the Theatre at Pompeii.
View of Vesuvius at Naples.
Temple of Jupiter at Pompeii.
Interior of the Temple of Mercury at
Pompeii.
Temple of Iris at Pompeii.
The Baker's House at Pompeii.
Altar of the Temple of Venus, Pompeii.
Sallust's House, Pompeii.
The Basilique at Poestum.
Gate of Herculaneum at Herculaneum.
The Right of the Forum, Pompeii.
The Pantheon at Pompeii.
Course of the Tombs at Pompeii.
Temple of Neptune at Poestum.
Temple of Ceres (No. 2) at Poestum.
Course of the Tombs at Pompeii.
Course of the Tombs (No. 2) Pompeii.
Chateau of Queen Jeanne at Naples.
•Walk of Fortune at Pompeii.
Castle of Baia, near Naples.
The Basilique at Pompeii.
The House of the Chapters at Pompeii.
View of the Forum at Pompeii.
The Three Temples at Poestum.
Temple of Venus at Pompeii.
House of Diomedes at Pompeii,
Temple of Venus at Naples.
St. Mary's at Palermo.
House of the Faun at Pompeii.
Stereoscopic Views in France, England, 6s. 6d. each.
„ „ Italy . . 7s. 6d.
,, ,, Rhine . . 7s. 6d.
The above are executed in Albumen on Glass by one of the first European
Artists, and in minuteness of detail and beauty of tone are the finest ever
issued. They are mounted with a Gold Fillet, and with full title upon each
picture.
The Departure— Bas-relief on the Arc de Tri-
omphe de FEtoile.
Glory— Bas-relief on the Arc de Triomphe de
l'Etoile.
War— Bas-relief on the Arc de Triomphe de
l'Etoile.
Peace— Bas-relief on the Arc de Triomphe de
l'Etoile.
Fountain Cuvier.
Arc de Triomphe de Carrousel.
Place de la Concorde (very good).
Apsis de Notre Dame de Paris (very good).
Exterior of the Church of St. Btienne du
Mont (very good).
Front view of the Palace of Justice, Paris.
Front view of the Terminus of the Stras-
bourg Railway.
Fore Court of the School of Beaux Arts,
Paris.
Palais des Tufleries.
The Madelaine (very fine).
Arc de Triomphe de l'Etoile.
Front view of the Church St. Vincent de
Paul.
New Sacristy of Notre Dame, Paris (very
good).
Fontaine Moliere.
The Clock Tower of the Palace of Justice,
Paris.
Notre Dame of Paris, View of the Quay des
Grands Augustins.
Perspective view of the Arc de Triomphe
de l'Etoile.
Fountain de la Place St. Sulpice.
8
Place du Chfitelet
Portal of Notre Dame, Paris (beautiful).
Notre Dame, Paris, south side (very good).
Front view of the Palais Royal.
View of the Quay de l'H6tel de Ville, Paris
(very good).
Quay of the Louvre.
View of the Seine, taken from the Pont
Royal (very good).
Notre Dame de Paris, and the bridge of the
Tournelle.
Notre Dame de Paris, north side (good).
Perspective view of the new Sacristy of
Notre Dame, Paris.
Front view of the Church of St Germain
l'Auxerrois.
Terminus of the Strasbourg Railway.
View of the Seine, taken from the Pont des
Arts.
Fountain in the Place Louvois.
Perspective du Quai et du Palais d'Orsay..
Colonne Vendome.
Interior of the Church of St. Btienne du
Mont.
Tower of Clovis, and Pantheon view of the
Polytechnic School.
Equestrian Statue of Louis XIV., Place des
Victoires.
Front view of the Pantheon.
Notre Dame and Hotel Dieu de Paris (very
good).
Front view of the Hotel de Ville, Paris (very
good).
Front view of the Hotel du Garde Meuble,
Paris.
View of the Seine, taken from the Fruit
Wharf (good).
Palace of the Luxembourg, garden frontage.
Palace du Luxembourg, et Tour St. Sulpice,
Lilac and Horse Chesnut Trees in bloom in
the garden of the Luxembourg.
Front view of the Hotel des Invalides.
Equestrian statue of Henry IV. view of the
Quai Conti.
View of the Pont Neuf, and perspective view
of the Louvre (good).
View of the Quai de l'Ecole.
Palais de Justice of Paris, View of the Quay
of the Me*giss£rie.
View of Pont Royal, et du Palais des
Tuileries.
The Louvre, view of the Platform du Pont
Neuf.
Villa du Quai d'Orsay.
The Mint, Paris.
Perspective view of the Chamber of Deputies.
Perspective view of the Seine with Drag
Boats (very fine).
View of the Cranes on the Wharf d'Orsay.
Poll Rouge & Notre Dame de Paris.
Perspective view of the Bridges on the
Seine (very fine).
Vue du Petit Pont sur la Seine.
Vue du Bains des Fleurs.
Perspective du Port Malaquais.
Dome des Invalides.
Circus in the Champs Elysees.
Gothic Pavilion in the Champs Elysees.
Fountain in the Champs Elysees.
Manage de Napoleon (very fine).
Cafe in the Champs ElyB&s, summer.
Chevaux de Marly.
View of the Seine, taken from the Quai de
la Conference.
Perspective view of the Church of St. Eus-
tache.
Southern frontage of the Church of St. Ens-
tache.
Front view of the Church of St. Gervais.
Sixteen different panoramic views of Paris.
Front view of the Hotel Cluny.
Colonnade of the Louvre.
View of the Entrance to the City of Paris.
Perspective view of the H8tel de Ville,
Paris.
Val de Grace.
View of the Institute, taken from the Quay
of the Louvre.
Front view of the Legislative Palace.
Cafe in the Champs Elysees, snow scene
(very beautiful).
Entrance to a Park in the Champs Elysees,
snow scene (very good).
Eleven Snow Scenes, taken from different
views at Trianon (all very beautiful).
Three different Landscapes on the Lake
of Enghien.
Chapel at the Palace of Versailles.
Statue of Louis XIV. at the Palace of Ver-
sailles.
Statue of Hoche at Versailles.
Front view of the Palace at Versailles.
Group of Lilac Trees in the Garden of the
Palace at Versailles.
Portal of the Church of St. Ouen at Rouen.
Statue of Joan of Arc at Rouen (very fine.)
Church of Notre Dame de Bon Secoure,
near Rouen.
Port of Rouen.
General view of Rouen, taken from the
Church of Bon Secours.
General view of the facade of Notre Dame,
of Rouen (very fine).
Four Panoramic Views of Rouen (various).
View of the Quay of the Island Lacroix at
Rouen.
Six views of the Ruins of the Abbey of
Jumieges, various (very interesting).
View of the Seine and the Court-yard of
Boyeldieu, Rouen.
Statue of Corneille, Rouen.
Porte Guillaume-Lion at Rouen.
Suspension Bridge, Rouen.
Portal of Notre Dame, Paris.
Entrance to the Place des Halles, Rouen
Place des Halles, Rouen.
Old Houses at Rouen.
Southern Angle of the Church of St. Ouen
at Rouen (beautiful).
Perspective view of the Church of St. Ouen
at Rouen.
Staircase of the Palais de Justice, Rouen.
Front view of the Palais de Justice, Rouen.
Perspective view of the Palais de Justice,
Rouen.
Porte des Cordeliers & Leches.
Front view of the Cathedral at Tours.
Castle of Uss6, Tuurraine.
Abbey of St. Denis.
Porte Dauphine at the Chateau de Fontaine-
bleau.
Southern Porch of the Cathedral at Chartres,
(beautiful).
Portion of the Southern Porch of the Cathe-
dral of Chartres.
Pont Guillaume at Chartres.
Pont de Massacre at Chartres.
Riviere des Trois Moulins at Chartres.
Ruins of the Church St. Andre* at Chartres.
Castle of Maintenon (very fine).
Portal of the Cathedral of Rheims (very
fine).
Northern side of the Cathedral of Rheims
(beautiful).
Southern side of the Church of St. Remi at
Rheims.
Place and Statue of Louis XV. at Rheims.
Interior of the Church St. Remi at Rheims.
Church of Notre Dame de l'Rpine.
Southern side of Notre Dame de l'Epine.
Southern side of the Cathedral of Stras-
bourg.
Southern Portal of the Cathedral of Stras-
bourg (very grand).
View of the Quay and Custom House at
Strasbourg.
View of the Island taken from the Custom
House Bridge at Strasbourg.
View of the Island taken from the Draw-
bridge at Strasbourg.
Panoramic View of Strasbourg.
Facade des Chevaliers at the Castle of Hei-
delberg (very interesting;.
Porte de la Facade des Chevaliers at the
Castle of Heidelberg (very interesting).
Clock Tower at the Castle of Heidelberg
(very interesting).
Galerie Robert at the Castle of Heidelberg
(very interesting).
Gallery of Antiquities at the Castle of
Heidelberg (very interesting).
Castle of Heidelberg as seen from the Park
Terrace (very interesting).
Castle of Heidelberg as seen from the Avenue
in the Park (very interesting).
General View of the Town of Heidelberg
(very interesting).
General View of the Castle of Heidelberg
(very -interesting).
The Bridge at Heidelberg (very interesting).
Porte de la Salle des Chevaliers at the
Castle of Heidelberg (very interesting).
Ruins of a Tower at the Castle of Heidel-
berg (very interesting).
Tower of the Sierre at the Castle of Heidel-
berg (very Interesting).
General View of Mayence.
Place Guttenberg at Mayence.
View of Mayence, taken from the opposite
Banks of the Rhine.
View of Rudesheim, Borders of the Rhine.
Western side of the Castle of Ehrenfels,
Borders of the Rhine.
Eastern side of the Castle of Ehrenfels,
Borders of the Rhine.
General View of Bingen, Borders of the
Rhine.
Castle of Rheinstein, Borders of the Rhine
(very beautiful).
Castle of Sonneck.
Castle of Falkenberg, Borders of the Rhine.
Castle of Furstemberg, Borders of the Rhine.
Rustic Cottage at Bacharach, Borders of the
Rhine.
Ruins of the Abbey at Bacharach.
General View of the Abbey at Bacharach.
View of Bacharach from the Vale.
View of Bacharach from the Rhine*
Castle of Pfalz.
View of Caub, from the opposite Banks of
the Rhine.
Castle of Giitenfels.
Castle of Oberwesel.
Large Tower of Oberwesel.
General view of Oberwesel.
Castle of St. Goar.
Castle of Stobzenfels, from the Upper Ter-
race.
Castle of Stobzenfels, from the Lower Ter-
race.
General View of Coblentz.
Church of Andernach.
Two Views of the Archiepiscopal Palace at
Andernach.
Ruins at Drachenfels.
The Rocks at Drachenfels.
Castle of Godesberg.
Southern Portal of the Cathedral of
Cologne (very beautiful).
Front Portal of the Cathedral of Cologne
(very good).
Apsis of the Cathedral of Cologne.
Porch of the Hotel de Ville at Cologne.
View of the Canal at Bruges.
View of the Canal Bridge at Bruges.
Police Station at Bruges.
View of the Chapel of St. Sang, Bruges.
Dock Yard at Boulogne.
The Quay at Boulogne.
Grand Rue, Boulogne.
Views of the Hills round Boulogne.
The Downs at Boulogne.
Facade of Westminster Abbey.
Guildhall.
Marble Arch.
The Wellington Aroh.
Facade of St. Paul's, London.
View of the Serpentine.
The Panopticon.
Charing Cross.
The Houses of Parliament from Westmin-
ster Bridge.
Suspension Bridge, and the Houses of
Parliament
10
The Queen's Entrance to the Houses of
Parliament.
A portion of the Houses of Parliament
The Houses of Parliament from the Thames.
Lambeth Palace.
Saint Clement's Church.
The Hone Guards.
Saint James's Park.
Statue of George IV., and Nelson's Column.
St. Paul's, from Southwark Bridge (very
good).
Tower of London (very good).
Bas-relief at Somerset House.
Statue of Charles I., at Trafalgar Square.
Temple Bar.
Interior of the Tower of London.
Side View of Westminster Abbey.
Fore Court of Somerset House.
Apsis of Westminster Abbey.
Eton College (very good).
Exterior of Windsor Castle.
Tower of Hercules at Windsor Castle.
The Round Tower at Windsor Castle.
Facade of Windsor Castle from the Terrace
(very beautiful).
General View of the Court Yard at Windsor
Castle.
8t. George's Tower, Windsor Castle.
Side View of Windsor Church.
Facade of Windsor Church.
General View of Windsor.
Greenwich Park.
Observatory at Greenwich (very good).
Two Views of Greenwich Hospital (good).
View of the Thames at Richmond.
Pope's Cottage at Twickenham.
Entrance to Hampton Court Palace.
Cedar of Libanus at Richmond.
Richmond Hill.
OrnamentalWater at Hampton Court.
Vessels at low water at Boulogne.
General View of Boulogne.
Passengers' Quay at Boulogne.
View of St. Rambert, near Lyons.
The Steeple of l'Dle Barbe.
General view of l'llle Barbe.
Chateau of l'llle Barbe.
The Centre of l'llle Barbe.
Perspective of the Saone at Lyons.
The Reserve at Marseilles.
View of Avignon.
View of Notre Dame de la Garde at Mar-
seilles.
Port of Toulon.
The New Port at Marseilles.
General view of Nice.
View of the Port at Nice.
Church of the Superga, Piedmont.
View of the Po at Turin.
Saint Charles's Place at Turin.
View of the Port of Genoa, No. 1.
View of the Port of Genoa, No. 2.
Port of Genoa, No. 8.
Port of Genoa. No. 4.
Ditto No. 5.
Ditto No. 6.
Palace of Doria and the Roadsteads of Genoa.
The Doorway of the Church, Carignano
Genoa.
View of the Pier at Genoa.
View of the Hills about Genoa, No. 1.
The Hills of Genoa, No. 2.
General View of Genoa.
Carignan Church at Genoa.
Cera Palace at Genoa.
General View of the Hospital at Genoa.
Descent from the Cross in the Church of
Saint Charles at Milan.
Panorama of Milan, No. 1.
Panorama of Milan, No. 2.
Palace of Justice at Milan.
Southern Side of the Dome of Milan.
Gate of the Ticmese%t Milan.
Interior of the Hospital at Milan.
Facade of the Dome at Milan.
Roman Gate at Milan.
Statue of Eve on the Dome at Milan, No. 1.
A Part of the Dome at Milan.
Facade of the Arc de la Paix at Milan.
Front of the Church St. Celse at Milan.
Part of the Dome at Milan.
Part of the Dome at Milan, No. 2.
Side View of the Arch of Peace at Milan.
General View of Como, No. 1.
General View of Como, No. 2.
General View of Como, No. 3.
General View of Como, No. 4.
View of Como taken from the Promenade.
Entrance to the Cathedral of Como (very fine).
Negretti's Villa at Como.
View of the Borgo Vico on the Lake of Como.
Side Entrance of Como Cathedral.
Facade of Como Cathedral.
Perspective of the Facade of the Dome of
Milan.
St. Ambroise Church at Milan.
Old Palace at Brescia.
The Church of St. Andrg-aVBrescia.
Panorama of Brescia, No. 1.
Panorama of Brescia, No. 2.
Panorama of Brescia, No. 3.
Hills about Brescia.
Entrance to the Monastery at Pavla.
Facade of the Monastery at Pa via.
The Left Side of the Monastery at Pavla.
Right Side of the Monastery of Pavia.
Vault of the Monastery of Pavia.
Southern side of the Monastery of Pavia.
Panorama of Padua, No. 1.
Panorama of Padua, No. 2.
Panorama of Padua, No. 3.
Church of St. Justine at Padua.
Antique Fountain at Brescia.
Palazzo del Capitano at Padua.
Facade of the Church St. Antoine, Padua.
Vault of the Cathedral, Padua.
La Loggia at Padua.
Perspective of North Side of the Palace of
Justice, Padua.
Perspective of South Side of the Palace of
Justice, Padua.
View of the Observatory at Padua.
11
Prato della Valle at Padua, No. 1.
Prato della Valle at Padua, No. 2.
Prato della Valle at Padua, No. 3.
Tomb of Antenor at Padua.
Statue of Barthelemie Calleoni at Venice.
Palace of Lacador at Venice.
View of the Grand Canal at Venice, No. 1.
View of the Grand Canal, Venice.
Bridge of Sighs at Venice, No. 1 (very beau-
tiful).
Bridge of Sighs at Venice, No. 2.
Front View of the Giant's Staircase at Venice
(beautiful).
Side View of the Giant's Staircase at Venice,
No. 1 (very beautiful).
Giant's Staircase at Venice, No. 2.
Facade of the Ducal Palace at Venice.
Perspective of the Zecca at Venice.
Perspective of St.Mark,and the Ducal Palace.
Facade of St. Mark at Venice.
Perspective of the Church of Salute at Venice.
General View of the Ducal Palace at Venice
(very good).
View of Venice taken from Canomia Bridge.
The Rialto at Venice.
View of Venice, taken from the Bridge of
the Rialto.
Front View of the Church of the Salute,
* Venice.
Ruins of the Palace of Lucrezia Borgia,
Venice (very fine).
Palace Papadapoli, Venice.
The Arsenal-Canal at Venice.
Perspective of the Ducal Palace, Venice.
Entrance to the Church of St. John and St.
Paul, Venice.
Garden of the Ducal Palace, Venice (very
good).
Quay of Esclavons at Venice.
Column of the Lion at St. Mark's, Venice
(beautiful).
Perspective of Courtyard of the Ducal Palace
at Venice.
View of the Razzitta at Venice.
Angle of the Ducal Palace, Venice (very fine).
General View of Venice, No. 1.
Ditto No. 2.
Ditto No. 3.
Ditto No. 4.
Ditto No. 5.
Ditto No. 6.
View taken from the Fisheries at Venice.
View of the Loggia at Venice (very good).
Entrance to the Arsenal at Venice.
Entrance to the Church of the Civil.
Hospital at Venice.
Church of St. Saviour, Venice.
Entrance to the Church of St. Mark, Venice.
View of St. George's Isle at Venice.
Palace Comaro Spinelli, Venice.
Palace Vcndramin, belonging to the Duchess
de Berri, at Venice.
Palace Grimani, Venice.
Palace Barbaro, Venice.
Palace Manin, Venice.
Interior of the Amphitheatre at Verona.
Exterior of the Amphitheatre at Verona.
Tomb of ScaligerL Verona, No. 1.
Tomb of SoaligerC Verona, No. 9.
Place St. Pierre, Mantua.
Statue of Ferdinand I., Florence.
Statue of Ferdinand L, Florence.
Dome of Florence.
Fountain of the Pitti Palace, Florence.
Panorama of Florence, No. 1.
Ditto No. 2.
Ditto No. 3.
Ditto No. 4.
Ditto No. 5.
Ditto No. 6.
Ditto No. 7.
The Rape of the Sabines, Florence.
The Cloisters of the Church of the Annun-
ciation at Florence.
View of Florence, taken from the Boboli
Gardens.
Group of Hercules Wiling the Centaur-
Florence.
General View of the Square of the Grand
Duke at Florence.
Perspective of the Interior of the Loge at
Florence.
A small Tower at Florence.
Perspective of the Fabrique des Offices,
Florence.
Giant's Fountain at Florence.
Neptune's Fountain in the Garden Boboli at
Florence.
View of Pitti Palace at Florence (very good).
Equestrian Statue of Come 1.— Florence.
Portion of the Loge at Florence.
Perspective of the Loge at Florence.
Statue of Perseus at Florence.
The Leaning Tower of Pisa (beautiful).
The Baptistery of Pisa, No. 1.
The Baptistery of Pisa, No. 2.
Pisa Cathedral (very fine).
Interior of Campo Santo, Pisa, No. 1.
Ditto No. 2.
Ditto No. 8.
Ditto No. 4.
Abside of Pisa Cathedral.
Cathedral of Lucques.
Castle and Bridge St. Angelo, at Rome.
Temple of Vesta, Rome.
Fountain of Trevi at Rome.
Fountain de la Place St. Pierre, Rome.
Monte Cavallo at Rome.
Arch of Janus, Rome.
Obelisque of the Place St. Pierre, Rome.
Cloisters of the Church of St. Paul, at Rome.
Ruins of the Temple of Venus, Rome.
Facade of the Capitol, Rome.
View of the Tiber, taken from the Port of
the Rissa Grande, Rome.
View of the Bridge Rocco, Rome.
View of the Tiber, taken from the Bank of
the Ghetto at Rome.
Fort St. Angelo, Rome (very good).
Isle of Tiberius, Rome.
Obelisque in the Place du Peuple, Rome.
Church of St. John Lateran, at Rome.
is
Temple of Antonius and Faustina, Rome.
Fountain de la Place Navona, Borne.
Bridge St. Angelo, at Borne (very good).
Church and Obelisgue of St. Pierre, at Rome.
View of Rome taken from the top of the
Staircase of the Capitol.
Obelisque in the Place da Peuple and the
Monte Pincio, Rome.
Statue of Marcos Aurelius at the Capitol,
Borne.
Fountain of Aqua Felice, Rome.
Church of St Maria Maggiore, Rome.
Facade of the Church of St. Pierre, Rome.
Arch of Titus. No. 1 (very good).
Arch of Titus. No. 2 (very good).
Arch of Constantino. No. I {very good).
Arch of Constantine. No. 2 (very good).
Temple of Peace, Rome (very good).
Arch of Septimus Severus, Rome (very good).
Arch and Aqueduct of Constantine.
Fountain of Monte Pincio, Rome.
Ruins of the Temple of Peace, Rome.
Column of Phocas, Rome.
Ruins of Temple of Jupiter, Rome (very fine).
Forum of Trajan, Rome.
Ruins of the Temple of Concord, Romt
(very fine).
Ruins of the Gnecostase, Rome.
General View of the Roman Town.
Place du Peuple, Borne.
General View of the Coliseum, Rome.
Interior of the Coliseum, No. 1.
Interior of the Coliseum, No. 2.
Interior of the Coliseum, No. 3.
Interior of the Coliseum, No. 4.
Panorama of Borne, No. 1.
Panorama of Borne, No. 2.
Panorama of Rome, No. 3.
Panorama of Borne, No. 4.
Panorama of Rome, No. 5.
Panorama of Rome, No. 6.
Panorama of Borne, No. 7.
Panorama of Rome, No. 8.
Panorama of Borne, No. 9.
Panorama of Rome, No. 10.
Port Bipetta, Rome.
Perspective of St. Mark's Church, Venice
(very beautiful).
Manin Palace, Venice.
SWITZERLAND, the PYRENEES, &c,
7s. 6d. each.
These are executed by the same artist as the preceding, and are of the most
beautiful and sublime character.
General View of Freyburg.
View of the Bridge at Basle.
Equestrian Statue of Rodolph D'Erlach at
Berne.
Grand Arch of the Bridge at Berne.
Panorama of Berne taken beneath the Quay
of the Aar.
Perspective of the Aar at Berne.
Side View of the Terrace at Berne.
View of the Church and Terrace at Berne.
Country View of Berne, taken from the Boof
of the Church (good).
Hotel de Ville at Berne.
View of the Lake at Thun.
A Cottage and the Church at Thun (very
good).
Peninsula of the Chateau of Rougemont, on
the Lake of Thun.
A Landscape on the Lake of Thun.
A Cottage and the Chateau of Thun.
View of Interlaken and the Jungfrau (good).
The Mills of Interlaken.
A Street in Interlaken.
View of Unterseen taken from the Goldei.
Torrent of Muhlilach, and the Church of
Brienz.
A Cottage and the Lake of Brienz.
A Street in Brienz.
The Alp of Brienz.
The Lake of Brienz.
A Street in Meiringen.
Fountain at Meiringen.
Upper Fall of the Reichenbach (very grand).
General View of Meiringen.
The Hills of Breiteumatt, seen from Mei-
ringen.
A Cottage at Meiringen.
Landscape in the Obscure Glen near Mei-
ringen.
Fall of the Staubbachat Lauterbrunnen (very
beautiful).
Cottages at Lauterbrunnen.
Falls of the Handeck (very good).
The Inn at Handeck.
View of the Aar, in front of the Falls of
Handeck.
View of the Bridge at Handeck (very good).
Torrent of the Smooth Bock near Handeck.
View of the Bridge Boegelein (very fine).
Pass of Boegelein near Handeck.
Cottages of Rosenlaui.
The Saw Mills of Rosenlaui (very good).
The Rocks and Foot Path at Bosenlaui.
The Grand Glacier of Bosenlaui (very grand).
The Lesser Glacier of Bosenlaui (most beau-
tiful).
13
View of Walhorn near Bosenlani.
Landscape taken on Wengernalp.
View of the Eiger taken from the Wen-
gernalp.
View of the Jungfrau taken from the Wen-
gernalp (very good).
Grand Glacier of Grindelwald.
Lesser Glacier of Grindelwald.
View of the Almhouses at Grimsel.
Avalanche of Stones near Grimsel.
View taken on the Glacier of the Aar (very
good).
Grand Glacier of the Rhone (very beautiful).
General View of the Glacier by the Rhone
(very beautiful).
View of Oberlegesten, Valley of the Rhone.
Valley of Viesch.
The Glaciers and Cottages of Viesch.
Village of Viesch.
The Church of Viesch.
View of Brieg, and the Simplon (very good).
Chateau of Brieg.
General View of Brieg.
Bridge of the Masta (very good).
The Edge of the Declivity of the Glacier of
Aletsch (very beautiful).
Village of Kemen, near the Glacier of Aletsch.
The Church of Viege, after the Earthquake.
Panorama of Sion (beautiful).
Ruins of the Chapel and Ch&teau of Sion.
View of the Valley of the Rhone at Sion.
Chapel of All Saints at Sion.
Mountain of the " Seminaire" at Sion.
Vane of the Church of Lausanne
Panorama of Lausanne (beautiful).
The Alarm Tower of Pribourg.
The Pass of the Sarine.
Chapel of Notre Dame de Bon Secours at
Fribourg
A Fountain at Fribourg.
Suspension Bridge at Fribourg.
Panorama of Fribourg, No. 1.
Panorama of Fribourg, No. 2.
Panorama of Fribourg, No. 3.
The Banks of the Sarine at Fribourg.
The Linden Tree of Morat, and the Hotel
de Ville of Fribourg.
View of the Valley of the Sarine.
A Cottage at Clarens, Lake of Geneva.
Statue of Jean Jacques Rousseau, at Geneva.
THE INUNDATIONS IN FRANCE (Several Plates).
THE LONDON STEREOSCOPIC COMPANY avail themselves of this
opportunity to submit the following series of Selections, which comprise every-
thing that can be desired by those desirious of possessing a collection of these
exquisite works of Art.
FIRST SELECTION.
A beautifully-finished Stereoscope, with all the recent improvements, mounted on an elegant
engine-turned stand, and ornamental base, with a choice collection of albumen and
collodion binocular views, from Padua, Milan, Venice, Pisa, Florence, the Rhine, Switzer-
land, Pompeii, &c, also celebrated works of Art from the Paris Exhibition and Crystal
Palace at Sydenham, together with a varied amusing collection of " Wilkie"-like
photographs, embracing almost every variety of human life, with a polished box,
suitable for any nobleman or gentleman's drawing-room table. The box, arranged
to contain the instrument and pictures, with crest engraved on the same if required,
20 Guineas.
SECOND SELECTION.
A collection, embracing all the preceding subjects, but proportionably decreased in number,
with an elegant mahogany Stereoscope and stand, and box for slides, 10 Guineas.
THIRD SELECTION.
An elegant selection from the above, with mahogany Stereoscope and box, without stand,
5 Guineas.
• The above trill be carefully packed and forwarded on receipt of remittance or check,
stating which Selection is preferred.
Selection*, with Instrument, for 21s. can be made if desired.
14
Description and Prices of Sir David Brewster's Lenticular -
Stereoscopes.
s. d.
I.— Japanned Tin Stereoscope, open at sides, front and bottom 2
2. — Plain Mahogany do. open in front and at bottom, with box eye pieces, from 3
Ditto, with brass eye-pieces, and superior lenses ... 6 6
3.— Polished do. do. with email door in front, open at bottom, and brass
adjusting mounts 7 6
4.— Do. do. Walnut or Sycamore Wood, ground glass at bottom,
brass mounts
5. — Do. do. do. sides curved
6. — Polished Mahogany Stereoscope, with horizontally shifting eye pieces ...
7. — Do. Rosewood do. do. do. do.
8.— Beautifully Polished Mahogany do., brass shifting and adjusting eye pieces,
reflecting flap at bottom, and small ivory spring to retain the slides 21 a
0.— Very Superior Rosewood or Mahogany, with patent adjusting screw and rack
work, sliding eye pieces
10. — Do. do. beautifully curved „
11. — Do. do. with all the above appliances, in beautifully
polished ebony, ivory patent screw, &c
12. — Beautifully inlaid Papier Mache' (a magnificent Wedding present)
13. — Book Stereoscopes, adapted for the pocket, carrying a dozen slides, if required...
14.— Just Out.— An. elegant new Patent Spring Folding Stereoscope (adapted for
travelling) 21
10
G
11
6
12
6
15
26
a
88
50
42
7
6
Tinted Papkbs, representing Morning, Noon, Evening, and 2fight, for colouring Trans-
parencies, Is. the set of four.
BOXES.
8. d.
Plain Mahogany box to hold Stereoscopic slides 5
Plain Mahogany box to hold Stereoscope and slides 10 6
Finely Polished Rosewood do. do. lined 31 6
The Stereoscopes can be mounted on telescopic brass stands for greater convenience of viewing
the objects, from 15s. to 2ls. each, extra. They are made so that the Stereoscope can
be detached at any time it is required separately.
Shippers and the Trade supplied.
OPERATORS IN COLLODION AND DAGUERREOTYPE.
STEREOSCOPIC PORTRAITS from 10s. to 31s. 6d.
Single Portraits of all sizes and beautifully Coloured.
15
STEREOSCOPIC CAMERAS
IS GREAT VARIETY.
PHOTOGKAPHIC APPARATUS AND CHEMICALS.
A Complete Set of Apparatus,
For taking Portraits or Views Stereoscopically,
Price, £6 6s.
The above Set is of the most perfect character, and supplies the Photo-
graphic Tourist with all the requisite Materials.
A Complete Set of Stereoscopic Apparatus, with
View and Portrait Lens,
Price, £10 10s.
The Apparatus, &c., of this Set is of a more finished character than the
above, and the Camera clamped with brass, packed in strong case, and is
admirably adapted for export to India, or other warm climates.
Photographic Camera,
With beautifully mounted double Achromatic Lens, taking Pictures and
Portraits 4J by 8£, with all the requisite Apparatus and Chemicals
packed in box, with lock and key.
Price, 46 6s.
Next Size Larger, taking Portraits 6j by 4J.
Price, £10 10s.
The Lenses of the above Sets of Apparatus are warranted, and for sharpness
and accuracy in their performance, are unsurpassed.
s. d.
Nitrate of Silver 3 11 peroz.
Iodized Collodion 8 per lb.
Plain do 7
Iodizing Solution 1 per oz.
For detailed List of Apparatus and Chemicals see Photographic Catalogue.
THE IMPROVED COLOUR REFLECTING STEREOSCOPE.
a Stop screw, by which the instrument is set to any convenient height.
b Hinge joint, on which the instrument is moved to any required angle.
e Adjusting pulley to regulate colour and light.
d The Colour reflector from which tints, as of Moonlight, Sunrise, Midday, and Sunset,
can be reflected on transparent pictures.
. e The eye pieces in which the optical arrangements are placed, and adjusted to variations
in focal distance, in the different conditions of sight.
A. P. 8haw, Trinter, 10, Devonshire Street, Bbhopegate, City.
Albemarle Street, London-.
July, 1856.
MR MURRAY'S
GENERAL LIST OF WORKS.
ABBOTT'S (Rev. J.) Philip Musgrave ; or, Memoirs of a Church of
England Missionary in the North American Colonies. Post 8vo. 2s. 64.
ABERCROMBIE'S (Johk, M.D.) Enquiries concerning the Intel-
lectual Powers and the Investigation of Truth. Fourteenth Edition.
Fcap.8vo. 6s. 6d.
Philosophy of the Moral Feelings. Tenth
Edition. Fcap. 8vo. 4s.
Pathological and Practical Researches on th*
Diseases of the Stomach, the Intestinal Canal, the Liver, and other
Viscera of the Abdomen. Third Edition, Fcap.Svo. 6*. .
ACLAND'S (Rbv. Charles) Popular Account of the Manners and
Customs of India, Illustrated with Numerous Anecdotes. Post8vo. 2*.6d.
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